Title: Current-to-voltage converting apparatus and impedance measuring apparatus
Abstract: A current-to-voltage converting apparatus connected to an element or a circuit having a first terminal connected to a signal source and comprising a feedback amplifier, which is connected to a second terminal of the element or the circuit and keeps the second terminal at virtual ground, and which converts the current signals that flow to the element or the circuit to voltage signals and outputs these signals; a device for opening the feedback loop of the feedback amplifier and measuring the open-loop loss of the feedback loop; and a compensating amplifier, which compensates for the open-loop loss. It further comprises a device for measuring the open-loop phase shift of the feedback loop when the feedback loop is open and a control unit for keeping the open-loop phase shift at a pre-determined value.
Patent Number: 7,005,918 Issued on 02/28/2006 to Iwasaki
| Inventors:
|
Iwasaki; Yukoh (Tokyo, JP)
|
| Assignee:
|
Agilent Technologies, Inc. (Palo Alto, CA)
|
| Appl. No.:
|
809262 |
| Filed:
|
March 25, 2004 |
Foreign Application Priority Data
| Apr 18, 2003[JP] | 2003-113733 |
| Current U.S. Class: |
330/107; 330/2; 324/601; 324/650 |
| Current Intern'l Class: |
H03F 1/36 (20060101) |
| Field of Search: |
330/107,2,9,85,86,109
327/560
324/601,602,548,649,650,658,672,686,76,77
|
References Cited [Referenced By]
U.S. Patent Documents
| 6054867 | Apr., 2000 | Wakamatsu.
| |
| 2002/0079959 | Jun., 2002 | Nair et al.
| |
| Foreign Patent Documents |
| 03-061863 | Mar., 1991 | JP.
| |
Primary Examiner: Shingleton; Michael B
Claims
What is claimed is:
1. A current-to-voltage converting apparatus connected to an element or a circuit
having a first terminal connected to a signal source, wherein said current-to-voltage
converting apparatus comprises:
a feedback amplifier, which is connected to a second terminal of said element
or said circuit and keeps said second terminal at virtual ground, and which converts
the current signals that flow to said element or said circuit to voltage signals
and outputs these signals,
means for opening the feedback loop of said feedback amplifier and measuring
the open-loop loss of said feedback loop, and
a compensating amplifier, which compensates for said open-loop loss.
2. The current-to-voltage converting apparatus according to claim 1, further comprising:
means for measuring the open-loop phase shift of said feedback loop when said
feedback loop is open; and
control means for keeping said open-loop phase shift at a pre-determined value.
3. The current-to-voltage converting apparatus according to claim 1, wherein
said feedback loop is open or the open-loop loss of said feedback loop is measured,
the output of said signal source is controlled so that it becomes zero or a direct-current signal.
4. The current-to-voltage converting apparatus according to claim 1, wherein
said feedback amplifier comprises a modulation-type narrow-band amplifier, and
said narrow-band amplifier comprises a quadrature detector, filters, and a vector modulator.
5. The current-to-voltage converting apparatus according to claim 4, wherein
said compensating amplifier is placed in between said quadrature detector and said
vector modulator.
6. The current-to-voltage converting apparatus according to claim 4, wherein
said control means controls the phase difference between the signal that is applied
to said quadrature detector and the signal that is applied to said vector modulator.
7. The current-to-voltage converting apparatus according to claim 4, wherein
said feedback loop is opened by being opened in between said quadrature detector
and said vector modulator.
8. The current-to-voltage converting apparatus according to claim 4, wherein
said feedback amplifier also comprises a null detector and feedback circuit,
said null detector is connected to said second terminal and the signals that
are input to said null detector are converted to voltage signals by the null detector,
said narrow-band amplifier resolves said converted voltage signal into an in-phase
component and an quadrature-phase component using said quadrature detector, filters
said in-phase component and said quadrature-phase component using said respective
filters, vector modulates said filtered in-phase component and said filtered quadrature-phase
component using said vector modulator, and outputs the vector voltage signals, and
said feedback circuit inputs said vector signals to said null detector.
9. The current-to-voltage converter apparatus according to claim 1, wherein said
element or said circuit is a capacitive element or capacitive circuit.
10. An impedance measuring apparatus which comprises:
a signal source connected to a first terminal of a device under test,
a feedback amplifier, which is connected to a second terminal of said device
under test and keeps said second terminal at virtual ground, and which converts
current signals that flow to said device under test to voltage signals and outputs
these signals,
means for opening the feedback loop of said feedback amplifier and measuring
the open-loop loss of said feedback loop,
a compensating amplifier, which compensates said open-loop loss, and
means for measuring the vector voltage ratio between the voltage signals between
said first terminal and said second terminal and the output signals of said feedback amplifier,
whereby it measures the impedance of said device under test from said vector
voltage ratio.
11. The impedance measuring apparatus according to claim 10, further comprising:
means for measuring the open-loop phase shift of said feedback loop when said
feedback loop is open; and
control means for keeping said open-loop phase shift at a pre-determined value.
12. The impedance measuring apparatus according to claim 10, wherein said feedback
loop is open or the open-loop loss of said feedback loop is measured, the output
of said signal source is controlled so that it becomes zero or a direct-current signal.
13. The impedance measuring apparatus according to claim 10, wherein said feedback
amplifier comprises a modulation-type narrow-band amplifier, and
said narrow-band amplifier comprises a quadrature detector, filters, and a vector modulator.
14. The impedance measuring apparatus according to claim 13, wherein said compensating
amplifier is in between said quadrature detector and said vector modulator.
15. The impedance measuring apparatus according to claim 13, wherein said control
means controls the phase difference between the signal that is applied to said
quadrature detector and the signal that is applied to said vector modulator.
16. The impedance measuring apparatus according to claim 13, wherein said feedback
loop is opened by being opened in between said quadrature detector and said vector modulator.
17. The impedance measuring apparatus according to claim 13, wherein said feedback
amplifier also comprises a null detector and feedback circuit,
said null detector is connected to said second terminal and the signals that
are input to the null detector are converted to voltage signals by the null detector,
said narrow-band amplifier resolves said converted voltage signal into an in-phase
component and an quadrature-phase component using said quadrature detector, filters
said in-phase component and said quadrature-phase component using said respective
filters, vector modulates said filtered in-phase component and said filtered quadrature-phase
component using said vector modulator, and outputs the vector voltage signals, and
said feedback circuit inputs said vector signals to said null detector.
18. The impedance measuring apparatus in claim 10, wherein said element or said
circuit is a capacitive element or capacitive circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an impedance measuring apparatus and in particular,
relates to an impedance measuring apparatus with which high-speed measurement is possible.
2. Background of the Art
Impedance measuring apparatuses that operate by the automatic balanced-bridge
method are an example of the prior art of impedance measuring apparatuses. Impedance
measuring apparatuses that operate by the automatic balanced-bridge method are
characterized in that they cover a broad measurement frequency range and their
measurement accuracy is good within a broad impedance measurement range.
The internal structure and operation of an impedance apparatus that operates
by the automatic balanced-bridge method are described below. FIG. 1 is a drawing
showing the internal structure of an impedance measuring apparatus that operates
by the automatic balanced-bridge method. Impedance measuring apparatus
10
in FIG. 1 comprises signal source
200, current-to-voltage converting apparatus
300, and vector voltmeter
400 for determining the impedance of device
under test
100. The entire impedance measuring apparatus
10 is operated
under the control of an operation control device CTRL
1 (not illustrated),
such as a CPU.
Device under test
100 is an element or a circuit having two terminals.
Device under test
100 should have at least two terminals and also, it can
be an element or a circuit with three or more terminals. In this case, two of the
three or more terminals are used for the measurements. Device under test
100
is represented by "DUT" in FIG. 1. The point where device under test
100,
cable
510, and cable
520 are connected in FIG. 1 is referred to as
the High terminal. Moreover, the point where device under test
100, cable
530, and cable
540 are connected is referred to as the Low terminal.
Signal source
200 is the signal source that is connected to a first
terminal of the device under test
100 by cable
510 and generates
measurement signals that are applied to device under test
100. Moreover,
signal source
200 is also connected to vector voltmeter
400 by cable
510, cable
520, and buffer
550 and feeds measurement signals
to vector voltmeter
400. The measurement signals are single sine-wave signals.
However, the measurement signals are not limited to single sine-wave signals and
can also be signals that comprise several sine waves.
Current-to-voltage converting apparatus
300 converts the
current that flows to device under test
100 and outputs voltage signals
to buffer
560. Current-to-voltage converting apparatus
300 comprises
a null detector
310, a narrow-band amplifier
600, a buffer
320,
and a range resistor
330. Cable
530, null detector
310, narrow-band
amplifier
600, buffer
320, range resistor
330, and cable
540
form a negative feedback loop
340.
Null detector
310 balances the current that flows to range resistor
330
and the current that flows to device under test
100 and outputs signals
to narrow-band amplifier
600 such that the current that flows into the input
terminals of null detector
310 through cable
530 will be brought
to zero. When the current that flows to range resistor
330 and the current
that flows to device under test
100 are balanced, the current at the Low
terminal is kept at virtual ground.
FIG. 2 is a drawing showing the internal structure of narrow-band amplifier
600. Narrow-band amplifier
600 comprises a phase sensitive detector
610, a filter
620 and a filter
630, as well as a vector modulator
640, and amplifiers and amplifies the output signals of null detector
310
and outputs them to buffer
320. Narrow-band amplifier
600 resolves
the output signals of null detector
310 into an in-phase component and an
quadrature-phase component using phase sensitive detector
610, filters the
in-phase component and quadrature-phase component using filter
620 and filter
630, modulates the filtered in-phase component and quadrature-phase component
using vector modulator
640, and feeds the vector-modulated voltage signals
to buffer
320.
Phase sensitive detector
610 is a quadrature detector and comprises
a mixer
611, a mixer
612, a signal source
613, and a signal
source
614. Signal source
613 generates sine-wave signals and feeds
them to mixer
611. Moreover, signal source
614 generates cosine-wave
signals and feeds them to mixer
612. The sine-wave signals output by signal
source
613 and the cosine signals output by signal source
614 have
the same frequency as the measurement signals and they are orthogonal to each other.
Consequently, mixer
611 and mixer
612 can orthogonally resolve the
output signal of null detector
310 into an in-phase component and an quadrature-phase component.
Filter
620 is an integrator that comprises a resistor
621, an
amplifier
622, and a capacitor
623, and integrates the output signals
of mixer
611. Filter
630 is an integrator comprising a resistor
631,
an amplifier
632, and a capacitor
633, and integrates the output
signals of mixer
612.
Vector modulator
640 comprises a mixer
641, a mixer
642,
a signal source
643, a signal source
644, and an adder
645.
Signal source
643 generates sine-wave signals and feeds them to mixer
641.
Moreover, signal source
644 generates cosine signals and feeds them to mixer
642. The sine-wave signals output by signal source
643 and the cosine-wave
signals output by signal source
644 have the same frequency as the measurement
signals, and they are orthogonal to each other. Mixer
641 modulates the
sine-wave signals that are output from signal source
643 with the output
signals of filter
620 and outputs the modulated sine signal. Mixer
642
modulates the cosine-wave signals output from signal source
644 with the
output signals of filter
630 and outputs the modulated cosine signal. The
voltage signals output from mixer
641 and the voltage signals output from
mixer
642 are added by adder
645 and output to buffer
320.
Vector voltmeter
400 of FIG. 1 measures output signal E
dut
of buffer
550 and output signal E
rr of buffer
560. Control
device CTRL
1 calculates the vector ratio of signal E
dut and
signal E
rr that have been measured and calculates the impedance of device
under test
100 from the calculated vector ratio and the resistance of range
resistor
330.
Measurement of the gate oxide film is one important measurement in the
production of MOS devices. The gate oxide film thickness is an important parameter
in determining the operating threshold of MOS-type devices. The gate oxide film
thickness is measured by measuring the impedance of an MOS device, calculating
the capacitance from the impedance measurement, and converting this calculated
capacitance to the equivalent oxide film thickness using the dielectric constant.
When an MOS device on a semiconductor wafer is tested using a conventional impedance
measuring apparatus
10, a wafer interface device comprising a switch matrix,
a chuck, a probe card, and the like is added between the impedance measuring apparatus
10 and device under test
100. The wafer interface device has a larger
ground capacitance than device under test
100. Moreover, cable
510,
cable
520, cable
530, and cable
540 that are connected between
this wafer interface device and impedance measuring apparatus
10 are relatively
long and also have a large ground capacitance. Cable
510, cable
520,
cable
530, and cable
540 are called cable
510, etc., hereafter.
FIG. 3 is a drawing in which the above-mentioned ground capacitance has been added
to FIG. 1. C
cable in FIG. 3 is the total ground capacitance of cable
510, etc. Moreover, C
winf is the ground capacitance of the wafer
interface device. The ground capacitance of the wafer interface device comprises
the ground capacitance of the switch matrix, the ground capacitance of the chuck,
and the ground capacitance of the probe card.
Conventional impedance measuring apparatus has two problems with high-speed
measurements. The first problem is that when a large ground capacitance is applied
to the Low terminal, the current-to-voltage converting apparatus
300 takes
a long time to settle. If the time to settling of the current-to-voltage converting
apparatus
300 is long, the time until the current that flows to range resistor
330 and the current that flows to the device under test are balanced is
also long and the wait time until measurements begin is increased. When the capacitance
of an MOS device on a semiconductor wafer is measured, this problem is exacerbated
by a wafer interface device and cable
510, etc., with a large ground capacitance,
as described above.
The second problem is that when the capacitance of an MOS device on a semiconductor
wafer is measured, the ground capacitance of the wafer interface device and cable
510, etc. is not constant. There are many types of wafer interface devices
and cable
510, etc. depending on the device under test and the user's selection.
Consequently, the ground capacitance of the wafer interface device and cable
510,
etc. is not constant. Unless the ground capacitance on the wafer interface device
and cable
510, etc. is constant, it will be very difficult to keep the ground
capacitance from affecting the measurement results as planned.
There has been considerable progress in microfabrication technology for semiconductors
in recent years, with a huge number of elements or circuits being formed on one
wafer. While there has been an obvious increase in the number of elements that
serve as the device under test, a corresponding increase in measurement time is
not allowed. Moreover, sacrifice of measurement precision for high-speed measurement
is not acceptable. The realization of high-speed, high-precision impedance measurement
is a very important problem in the semiconductor industry today.
SUMMARY OF THE INVENTION
The present invention provides a novel apparatus with which impedance can be
measured at high speed and high precision in order to solve the above-mentioned problems.
The present invention was created in order to realize the above-mentioned object.
The present invention is characterized in that it is a current-to-voltage converting
apparatus connected to an element or a circuit having a first terminal connected
to a signal source comprising a feedback amplifier, which is connected to a second
terminal of this element or this circuit and keeps this second terminal at virtual
ground, and converts current signals that flow to this element or this circuit
to voltage signals and outputs these signals; means for opening the feedback loop
of this feedback amplifier and measuring the open-loop loss of this feedback loop;
and a compensating amplifier, which compensates for this open-loop loss.
Moreover, the present invention also provides an impedance measuring apparatus
characterized in that it comprises a signal source connected to a first terminal
of a device under test; a feedback amplifier, which is connected to a second terminal
of this device under test and keeps this second terminal at virtual ground, and
converts to voltage signals and outputs the current signals that flow to this device
under test; means for opening the feedback loop of this feedback amplifier and
measuring the open-loop loss of this feedback loop; a compensating amplifier, which
compensates this open-loop loss; and means for measuring the vector voltage ratio
between the voltage signals between this first terminal and this second terminal
and the output signals of this feedback amplifier; and it measures the impedance
of this device under test from this vector voltage ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a drawing showing the internal structure of an impedance measuring
apparatus of the prior art.
FIG. 2 is a drawing showing the internal structure of a narrow-band amplifier
of an impedance measuring apparatus of the prior art.
FIG. 3 is a drawing showing an impedance measuring apparatus of the prior art
to which a wafer interface apparatus has been added.
FIG. 4 is a drawing showing the internal structure of the impedance measuring
apparatus of the present invention.
FIG. 5 is a drawing showing the internal structure of the narrow-band amplifier
of the impedance measuring apparatus of the present invention.
FIG. 6 is a flow chart showing the operation of the impedance measuring apparatus
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described based on the preferred embodiments
shown in the appended drawings. The first embodiment of the present invention is
an impedance measuring apparatus that operates by the automatic balanced-bridge
method, and its internal structure is shown in FIG. 4. The same reference symbols
are used in FIGS. 1 and 4 for structural elements having the equivalent function
and properties.
An impedance measuring apparatus
20 in FIG. 4 comprises a signal source
200, a current-to-voltage converting apparatus
800, and a vector
voltmeter
400 for measuring the impedance of device under test
100.
Impedance measuring apparatus
20 operates under the control of computer
device CTRL
2 (not illustrated) that executes the programs.
Device under test
100 comprises multiple MOS devices on a semiconductor
wafer. For convenience, the device under test is represented in the drawing as
only one "DUT." The MOS capacitance of the MOS device is measured in the present
embodiment and therefore, device under test
100 is a capacitor with a first
terminal and a second terminal. Device under test
100 is connected to impedance
measuring apparatus
20 through a wafer interface device
700. Although
not illustrated, wafer interface device
700 comprises a switch matrix, a
chuck, a probe card, and the like. The point where wafer interface device
700
and a cable
510 and a cable
520 are connected is referred to as the
High terminal. Moreover, the point where wafer interface device
700 and
cable
530 and a cable
540 are connected is referred to as the Low
terminal. Device under test
100 should have at least two terminals and also
can be an element or circuit with three or more terminals, such as a transistor.
In this case, two of the three or more terminals are used in the measurements.
Signal source
200 is the signal source that is connected to the first
terminal of device under test
100 via cable
510 and wafer interface
device
700 and generates the measurement signals that will be applied to
device under test
100. Moreover, signal source
200 is the signal
source that is connected to vector voltmeter
400 through cable
510,
cable
520, and buffer
550 and feeds the measurement signals to vector
voltmeter
400. The measurement signals are single sine-wave signals. However,
the measurement signals are not limited to single sine-wave signals and can also
be signals that comprise multiple sine waves.
A current-to-voltage converting apparatus
800 converts current flowing
to
device under test
100 and outputs voltage signals to buffer
560.
Current-to-voltage converting apparatus
800 comprises a null detector
310,
a narrow-band amplifier
900, a buffer
320, and a range resistor
330.
Cable
530, null detector
310, narrow-band amplifier
900, buffer
320, range resistor
330, and cable
540 form a negative feedback
loop
810.
Null detector
310 balances the current that flows to range resistor
330
and the current that flows to device under test
100 and outputs signals
to narrow-band amplifier
900 so that the current that flows through cable
530 to the input terminal of null detector
310 is brought to zero.
When the current that flows to range resistor
330 and the current that flows
to device under test
100 are balanced, the voltage of the Low terminal is
kept at virtual ground.
FIG. 5 is a drawing showing the internal structure of narrow-band amplifier
900. Narrow-band amplifier
900 comprises a phase sensitive detector
910, filters
920 and
930, a variable gain amplifier
941,
a variable gain amplifier
942, a switch
951, a switch
952,
a constant voltage source
961, a constant voltage source
962, a vector
modulator
970, a switch
980, and a switch
990, and amplifies
the output signals of null detector
310 and outputs them to buffer
320.
Phase sensitive detector
910 is quadrature detector and comprises a
mixer
911, a mixer
912, a signal source
913, and a signal
source
914. Signal source
913 generates sine-wave signals and feeds
them to mixer
911. Moreover, signal source
914 generates cosine signals
and feeds them to mixer
912. The sine-wave signals output by signal source
913 and the cosine-wave signals output by signal source
914 have
the same frequency as the measurement signals and the signals are orthogonal to
each other. Consequently, mixer
911 and mixer
912 orthogonally resolve
the output signal of null detector
310 into an in-phase component and an
quadrature-phase component and output the signals to filter
920 and filter
930. The output signal of signal source
913 and the output signal
of signal source
914 should be signals that have the same frequency as the
measurement signal and are orthogonal to each other, and they can be a rectangular-wave
signal rather than a sine-wave signal.
Filter
920 is an integrator comprising a resistor
921, an amplifier
922, and a capacitor
923, and integrates the output signals of mixer
911. Moreover, filter
930 is an integrator comprising a resistor
931, an amplifier
932, and a capacitor
933, and integrates
the output signals of mixer
912.
Variable gain amplifier
941 amplifies the output signals of filter
920 and outputs them to switch
951. Moreover, variable gain amplifier
942 amplifies the output signals of filter
930 and outputs them to
switch
952. The gain of variable gain amplifier
941 and that of variable
gain amplifier
942 are the same and the gain is changed by computer control CTRL
2.
Switch
951 selects either the output signals of variable gain amplifier
941 or the output signals of constant voltage source
961 and outputs
these to vector modulator
970. Moreover, switch
952 selects either
the output signals of variable gain amplifier
942 or the output signals
of constant voltage source
962 and outputs them to vector modulator
970.
Vector modulator
970 comprises a mixer
971, a mixer
972,
a signal source
973, a signal source
974, and an adder
975.
Signal source
973 generates sine-wave signals and feeds them to mixer
971.
Moreover, signal source
974 generates cosine-wave signals and feeds them
to mixer
972. The sine-wave signals output by signal source
973 and
the cosine-wave signals output by signal source
974 have the same frequency
as the measurement signals and are orthogonal to each other. Mixer
971 modulates
the sine-wave signals output from signal source
973 with the output signals
of switch
951 and outputs the modulated sine signal. Mixer
972 modulates
the cosine-wave signals output from signal source
974 with the output signals
of switch
952 and outputs the modulated cosine signal. The voltage signals
that are output from mixer
971 and the voltage signals that are output from
mixer
972 are added by adder
975 and output to buffer
320.
The output signals of signal source
973 and the output signals of signal
source
974 should be signals having the same frequency as the measurement
signals and that are orthogonal one another. They are not limited to sine-wave
signals or cosine-wave signal. For instance, rectangular-wave signals can be used
in place of these signals.
Switch
980 feeds the signals that will be input to phase sensitive
detector
910 to vector voltmeter
400 as necessary. Moreover, switch
990 feeds the output signals of mixer
971 to vector voltmeter
400
as necessary.
Vector voltmeter
400 of FIG. 4 measures output signal E
dut
of buffer
550 and output signal E
rr of buffer
560. Control
device CTRL
2 calculates the vector ratio of measured signal E
dut
and signal E
rr and further, calculates the impedance of device
under test
100 from the calculated vector ratio and the resistance of range
resistor
330. Although not illustrated, range resistor
330 comprises
multiple resistors with different resistances and selects the resistor as needed
in accordance with the impedance of device under test
100 that is to be
measured. Impedance measuring apparatus
20 thereby can measure the impedance
from a wide range of values.
Next, the operating procedure of impedance measuring apparatus
20 will
be described. As previously explained, impedance measuring apparatus
20
is operated under the control of computer device CTRL
2 that executes
the programs. Consequently, the following operating procedure describes the flow
of the program executed by computer device CTRL
2. The flow chart that
shows the operating procedure of impedance measuring apparatus
20 is shown
in FIG. 6.
First, at step
10, impedance measuring apparatus
20 initializes
the entire device. For instance, it performs voltage offset adjustment within the
apparatus, and the like.
Next, at step
20, negative feedback loop
810 is opened, the adjustment
signals for measuring the open-loop loss and the open-loop phase shift of the negative
feedback loop are output and the adjustment signals (original signals) are measured.
The open-loop loss and open-loop phase shift are the loss and the phase of the
one-loop transmission function. Specifically, the output signals of signal source
200 become zero or direct current signals constant-voltage source
961
and mixer
971 are conducted with switch
951 as the A side and constant
voltage source
962 and mixer
972 are conducted with switch
952
as the A side. When signal source
200 becomes either zero or a direct-current
signal, the High terminal is grounded. Sine-wave signals are output from signal
source
973. Zero or direct current signals are output from signal sources
974. The output signals of mixer
971 are used as the adjustment signals
for this condition. Furthermore, switch
990 is turned on and the vector
voltage of the adjustment signals is measured by vector voltmeter
400.
Next, in step
30, the signals for adjustment that have gone through
one negative feedback loop are measured with negative feedback loop
810
left open. Specifically, switch
990 is turned off and switch
980
is turned on. Moreover, the vector voltage of the signals for adjustment that have
gone through one negative feedback loop is measured by vector voltmeter
400.
Next, at step
40, the open-loop loss and the open-loop phase shift are
calculated, the open-loop loss is compensated, and the open-loop phase shift is
brought to the pre-determined value. Specifically, the ratio of the amplitude of
the vector voltage and the difference in the phase angles of the vector voltage
are found by comparing the vector voltage measured at step
20 and the vector
voltage measured at step
30. The ratio of the amplitude of the vector voltage
is the open-loop loss and the difference in the phase angles of the vector voltage
is the open-loop phase shift. In order to compensate for the open-loop loss, the
gain of the variable gain amplifier
941 and the gain of variable gain amplifier
942 are set by being multiplied by the inverse of the open-loop loss. Moreover,
the phase of the output signals of signal source
913 and the phase of the
output signals of signal source
914 are controlled in order to keep the
open-loop phase shift at a pre-determined value. Negative feedback loop
810
settles most rapidly when the open-loop phase shift is 180°. In other words,
the time up to when measurements start is shortened. Consequently, the phase of
the output signals of signal source
913 and the phase of the output signals
of signal source
914 are controlled so that the value obtained by subtracting
180° from the open-loop phase shift is desired open-loop phase shift φ.
By compensating for open-loop loss and controlling the open-loop phase shift as
described above, the settling time of negative feedback loop
810 is uniform
and can be universally shortened at all of the measurement signal frequencies,
regardless of the impedance of device under test
100 that is connected,
the ground capacitance of wafer interface device
700, the total ground capacitance
of cable
510, and the frequency of the measurement signals, and therefore
the output signal of current-to-voltage converting apparatus
800 settles
rapidly. As above mentioned, control of the open-loop phase shift is performed
by controlling the phase of the output signals of signal source
913 and
the phase of the output signals of signal source
914. Control of the open-loop
phase shift can also be performed by controlling the phase of the output signals
of signal source
973 and the phase of the output signals of signal source
974.
Next, at step
50, negative feedback loop
810 is closed and the
impedance of device under test
100 is measured. Specifically, switches
951
and
952 are brought to the T side and variable gain amplifier
941
and mixer
971 are connected and variable gain amplifier
942 and mixer
972 are connected, respectively. Cosine signals are output from signal source
974. Switch
980 and switch
990 are both turned off. The output
signal E
dut of buffer
550 and the output signal E
rr of
buffer
560 are measured by vector voltmeter
400. Furthermore, the
vector ratio of the measured signal E
dut and the signal E
rr is
calculated and the impedance of device under test
100 is calculated from
the calculated vector ratio and the resistance of range resistor
330.
Next, at step
60, the calculated impedance is output to the display
screen (not illustrated), or is output to the printer (not illustrated) that is
connected to impedance measuring apparatus
20 or the like.
The above-mentioned embodiment of the present invention is only one embodiment
that explains the present invention according to the Scope of the Patent Claim,
and it is clear to experts in the field that a variety of modifications are possible
within the claimed scope of the Scope of the Patent Claim. Finally, several embodiments
of the present invention are given below, underscoring the possibility of broad
application of the present invention.
A current-to-voltage converting apparatus characterized in that it is a current-to-voltage
converting apparatus connected to an element or a circuit having a first terminal
connected to a signal source, with this current-to-voltage converting apparatus
comprising: a feedback amplifier, which is connected to a second terminal of this
element or this circuit and keeps this second terminal at virtual ground, and which
converts the current signals that flow to this element or this circuit to voltage
signals and outputs these signals, means for opening the feedback loop of this
feedback amplifier and measuring the open-loop loss of this feedback loop, and
a compensating amplifier, which compensates for this open-loop loss.
The current-to-voltage converting apparatus as discussed above, characterized
in that it further comprises: means for measuring the open-loop phase shift of
this feedback loop when this feedback loop is open; and control means for keeping
this open-loop phase shift at a pre-determined value.
When this feedback loop is open or the open-loop loss of this feedback loop
is measured, the output of this signal source is controlled so that it becomes
zero or a direct-current signal.
The feedback amplifier preferably comprises a modulation-type narrow-band amplifier,
and this narrow-band amplifier comprises a phase sensitive detector, filters, and
a vector modulator.
The compensating amplifier is placed in between the phase sensitive detector
and the vector modulator.
The control means controls the phase difference between the signal that is applied
to the phase sensitive detector and the signal that is applied to the vector modulator.
The feedback loop is opened by being opened in between the phase sensitive detector
and the vector modulator.
The feedback amplifier further comprises a null detector and a feedback circuit,
the null detector is connected to the second terminal and the signals that are
input to the null detector are converted to voltage signals by the null detector,
the narrow-band amplifier resolves this converted voltage signal into an in-phase
component and an quadrature-phase component using the phase sensitive detector,
filters this in-phase component and this quadrature-phase component using these
respective filters, vector modulates this filtered in-phase component and this
filtered quadrature-phase component using this vector modulator, and outputs the
vector voltage signals, and the feedback circuit inputs these vector signals to
the null detector.
The element or circuit is a capacitive element or capacitive circuit.
An impedance measuring apparatus which comprises: a signal source connected to
a first terminal of a device under test, a feedback amplifier, which is connected
to a second terminal of the device under test and keeps the second terminal at
virtual ground, and which converts current signals that flow to this device under
test to voltage signals and outputs these signals, means for opening the feedback
loop of this feedback amplifier and measuring the open-loop loss of this feedback
loop, a compensating amplifier, which compensates this open-loop loss, and means
for measuring the vector voltage ratio between the voltage signals between the
first terminal and the second terminal and the output signals of the feedback amplifier,
wherein it measures the impedance of the device under test from this vector voltage ratio.
The impedance measuring apparatus further comprising: means for measuring the
open-loop phase shift of the feedback loop when this feedback loop is open; and
control means for keeping the open-loop phase shift at a pre-determined value.
The feedback loop is open or the open-loop loss of this feedback loop is measured,
the output of the signal source is controlled so that it becomes zero or a direct-current signal.
The feedback amplifier comprises a modulation-type narrow-band amplifier, and
this narrow-band amplifier comprises a phase sensitive detector, filters, and a
vector modulator.
The compensating amplifier is placed in between the phase sensitive detector
and the vector modulator.
The control means controls the phase difference between the signal that is applied
to the phase sensitive detector and the signal that is applied to the vector modulator.
The feedback loop is opened by being opened in between the phase sensitive detector
and the vector modulator.
The feedback amplifier further comprises a null detector and a feedback circuit,
this null detector is connected to the second terminal and the signals that are
input to the null detector are converted to voltage signals by the null detector,
the narrow-band amplifier resolves this converted voltage signal into an in-phase
component and an quadrature-phase component using the phase sensitive detector,
filters this in-phase component and this quadrature-phase component using these
respective filters, vector modulates this filtered in-phase component and this
filtered quadrature-phase component using the vector modulator, and outputs the
vector voltage signals, and the feedback circuit inputs these vector signals to
the null detector.
The element or the circuit is a capacitive element or capacitive circuit.
As previously described in detail, a current-to-voltage converting apparatus
connected
to an element or a circuit having a first terminal connected to a signal source
comprises a feedback amplifier, which is connected to a second terminal of this
element or this circuit and keeps the second terminal at virtual ground, and which
converts the current signals that flow to this element or this circuit to voltage
signals and outputs these signals; means for opening the feedback loop of this
feedback amplifier and measuring the open-loop loss of this feedback loop; and
a compensating amplifier, which compensates for this open-loop loss, and therefore,
the settling time of this feedback loop is shortened.
In addition, it comprises means for measuring the open-loop phase shift of the
feedback loop when this feedback loop is open and control means for keeping this
open-loop phase shift at a pre-determined value, and therefore, the settling time
of this feedback loop is further shortened.
The result of shortening the settling time of this feedback loop is similarly
obtained with the impedance measuring apparatus comprising the above-mentioned
current-to-voltage converting apparatus. That is, the impedance measuring apparatus
comprises a signal source connected to a first terminal of a device under test;
a feedback amplifier, which is connected to a second terminal of this device under
test and keeps the second terminal at virtual ground, and which converts current
signals that flow to this device under test to voltage signals and outputs these
signals; means for opening the feedback loop of this feedback amplifier and measuring
the open-loop loss of this feedback loop; a compensating amplifier, which compensates
this open-loop loss; and means for measuring the vector voltage ratio between the
voltage signals between the first terminal and the second terminal and the output
signals of this feedback amplifier. Therefore, the settling time of this feedback
loop can be shortened and high-speed measurement is possible.
Moreover, the vector measuring apparatus comprises means for measuring
the open-loop phase shift of this feedback loop when this feedback loop is open
and control means for keeping this open-loop phase shift at a pre-determined value.
Therefore, the settling time of this feedback loop is further shortened and measurements
can be conducted more rapidly.
For instance, when the device under test is a capacitor of 10 pF and the ground
capacitance of the wafer interface device is 1,000 pF or higher and the impedance
of the device under test is measured at a measurement signal of 100 kHz, the measurement
time of the impedance measuring apparatus of the present invention proceeds at
least three times more rapidly than that of a conventional apparatus.
*
