Senior Fitness - Exercise and Nutrition for Aging Men and Women
FREE Article Feed for your website.
Home Ownership Magazine
Party Planning Information
Article Marketing Resources
Bio-Medical Research Article Database
Informative Articles on Life, Love and Happiness
Tutorials on Business to Writing
Famous Quotes from Famous People
Song Lyric Information
New US Patent Information
Comprehensive List of Content by Category
Online Auctions and Shopping Related Articles
Article Search
Most Recent Articles
 

Getting the Best Business Credit Card for Your Company
Category:
Finance / Investment  

Discover How to Stop Hair Loss Grow More Hair
Category:
Health / Fitness  

Separation Anxiety
Category:
Health / Fitness  

Visit Stuttgart to discover a city of easy contrast
Category:
Travel  

Home Typing Jobs Paid Per Assignment
Category:
Business  

crying baby
Category:
Home And Family  

Reshape Your Body Attraction with Phentermine
Category:
Health / Fitness  

Conflict Leadership And The Leadership Talk
Category:
Business  

Cash out refinance Turning lemons into lemonade
Category:
Finance / Investment  

Asthma Natural Remedies With no Side Effects
Category:
Health / Fitness  

Affiliate Cloaking What It IS And WHY You Should Be Using It If ...
Category:
Business  

Peers and Power Are a Potent Mix
Category:
Business  

The Simple Truth About Content Writing
Category:
Marketing  

Strength Training Gets Everyone Lean and Fit
Category:
Health / Fitness  

The Role of a Medical Malpractice Attorney
Category:
Health / Fitness  

How to Grab Those Current Broadway Shows and Tickets
Category:
Entertainment / Television  

5 Proven Tips For Network Marketing Success
Category:
Marketing  

Essential Money Management Strategies For Horse Betting
Category:
Sports  

Come in to life again with cialis
Category:
Health / Fitness  

Why You Should Reject Most Credit Card Offers
Category:
Business  

Mangosteen Xanthones and Antioxidants
Category:
Health / Fitness  

Why affiliate marketers should use Google Adsense
Category:
Marketing  

Madonna Confesses Dance Floor Tour May Be Coming
Category:
Entertainment / Television  

Spyware Has Your Computer Been Infected
Category:
Computers  

The Income opportuneness provable to make money online
Category:
Business  

Generic Cialis Branded Solution For Your Problem
Category:
Health / Fitness  

free ringtones
Category:
Pets  

How Opt in Email Marketing Is Still A Marketing Tool To Remember...
Category:
Marketing  

Park City Utah Winter Activities
Category:
Travel  

Life Insurance Plan Online 7 Terms You Should Know
Category:
Finance / Investment  

Performing Successful Data Recovery For Computers
Category:
Computers  

Keeping Moisture Out Of Your House
Category:
Home And Family  

How To Maximize Your Aerobics Workout
Category:
Health / Fitness  

Food Processing Industry in China Expanding Fast
Category:
Business  

Want to Get a New Job Before 2007 Sets in Part Two
Category:
Business  

Five Important Things You Sould Know Before Visiting Costa Rica
Category:
Travel  

Web designing Is your website doing business
Category:
Computers  

Add A Gourmet Taste With Cilantro
Category:
Food / Drink  

Artists Create New Music Specially for Cell Phones
Category:
Business  

What Everyone Needs to Know about High Blood Pressure
Category:
Health / Fitness  

Zero Down Payment On Georgia Homes Offered By Investor
Category:
Finance / Investment  

7 Ways To Convert Your Traffic Into Cash
Category:
Marketing  

Scanning Images Made Simple In 5 Steps
Category:
Computers  

Mortgage Insurance Protects Bank Forced Repossess Your House Los...
Category:
Business  

Secrets To A Successful Carpet Cleaning Business
Category:
Business  

Guerrilla Marketing for the Small Marketing Budget
Category:
Marketing  

My Baseball Appreciation List
Category:
Sports  

Making Money Online What are you doing
Category:
Marketing  

Find Keywords with this Cutting Edge Strategy
Category:
Business  

Orchid Plants
Category:
Home And Family  

Small Business 10 Key Attributes Your Sales Staff Must Have
Category:
Business  

Vitamin A
Category:
Health / Fitness  

How To Play Guitar Free Online Guitar Lesson
Category:
Entertainment / Television  

Securing a personal loan is much easier when you know what optio...
Category:
Finance / Investment  

Tips To Selecting The Right Acne Medicine
Category:
Health / Fitness  

Used Bicycles Sustainability Anyone
Category:
Sports  

Google Adwords Writing Secrets you Need to Know
Category:
Marketing  

Cellular Phones Can they effect your life
Category:
Business  

The Best Fixer Upper Home Contractor Tips to Find One
Category:
Business  

Beer Through the Years
Category:
Food / Drink  

Ringtones Choosing Your Ringtone Type
Category:
Entertainment / Television  

the principles of scientific cookery
Category:
Health / Fitness  

For the Air and Space Enthusiast
Category:
Hobbies / Pastimes  

How Honda Screwed Up The Internet Marketer s Logic And How You C...
Category:
Marketing  

Cheap futon Cheap and Elegant goes hand in hand in the shape of ...
Category:
Home And Family  

What are no load mutual funds
Category:
Finance / Investment  

Now Yurt talking
Category:
Travel  

Advantages and disadvantages of using web templates or WYSIWYG e...
Category:
Self Help  

Fertile Ground
Category:
Health / Fitness  

Do Cosmetics Causes Acne
Category:
Health / Fitness  

What You Need To Know Before Refinancing Your Mortgage
Category:
Business  

Home Loans and Loan Interest Rates
Category:
Finance / Investment  

Adjustable Rate Mortgages vs Fixed Rate Mortgages
Category:
Business  

Quality Of Cosmetic Organizers
Category:
Health / Fitness  

Choosing a used car dealership in Texas
Category:
Education

Apparatus and method for charge pump slew rate control Number:7,365,585 from the United States Patent and Trademark Office (PTO) owispatent

Home    Author Login    Submit Article    Article Search    Add Your Link    Edit Your Link    Contact Us    Advertising    Disclaimer

   

 
Web LinkGrinder.com

Top Breaking News
     Woods Seizes Lead in AT&T Golf by David Byrd
     Honduras Court Rebuffs OAS on Zelaya's Return  by Brian Wagner
     North Korea Fires Three Missiles by VOA News

Title: Apparatus and method for charge pump slew rate control

Abstract: An apparatus and method for improving memory cell reliability is disclosed. The slew rate is reduced in an applied voltage signal used to program a memory cell when Fowler-Nordheim (FN) tunneling injection is detected. The applied programming signal is provided by a charge pump that is preferably a regulated charge pump. The charge pump is selectively controlled by a slew rate control circuit when FN tunneling injection is detected by a voltage level detection circuit at a predetermined threshold voltage level.

Patent Number: 7,365,585 Issued on 04/29/2008 to Fort,   et al.


Inventors: Fort; Jimmy (Aix-en-Provence, FR), Daga; Jean-Michel (Peynier, FR)
Assignee: Atmel Corporation (San Jose, CA)
Appl. No.: 11/501,798
Filed: August 9, 2006


Current U.S. Class: 327/170 ; 326/29; 326/31; 327/387; 327/540; 327/80
Current International Class: H03K 5/12 (20060101)


References Cited [Referenced By]

U.S. Patent Documents
4685083 August 1987 Leuschner
5359552 October 1994 Dhong et al.
5596532 January 1997 Cernea et al.
5638007 June 1997 Sabin
5693570 December 1997 Cernea et al.
5742193 April 1998 Colli et al.
5768208 June 1998 Bruwer et al.
5818766 October 1998 Song
5828245 October 1998 Brambilla et al.
5939909 August 1999 Callahan, Jr.
5949259 September 1999 Garcia
6127880 October 2000 Holst et al.
6154101 November 2000 Zou et al.
6388505 May 2002 Ribellino et al.
6483377 November 2002 White et al.
6492686 December 2002 Pappert et al.
6646415 November 2003 Nebrigic et al.
6788608 September 2004 Tran et al.
6801080 October 2004 Arcus
6819163 November 2004 Gregoire, Jr.
6836179 December 2004 Mizuno et al.
6859391 February 2005 Combe et al.
6914476 July 2005 Ingino, Jr.
6992934 January 2006 Sarin et al.
6992937 January 2006 Tran et al.
6998891 February 2006 Hsu et al.
7015721 March 2006 Nguyen et al.
7035151 April 2006 Tran et al.
7049872 May 2006 Diorio et al.
7061295 June 2006 Saiki et al.
7250810 July 2007 Tsen et al.
2004/0251955 December 2004 Neidorff
2005/0134244 June 2005 Sanzo et al.
2005/0219903 October 2005 Daga
2006/0123280 June 2006 Tran et al.

Other References

Horace G. Jackson et al. "Analysis and Design of Digital Integrated Circuits: In Deep Submicron Technology. Thid Edition. Semiconductor Memory Design" (2004) 359-398. cited by other .
P. Canet et al. "Improvement of EEPROM cell reliability by optimization of signal programming." Journal of Non-Crystalline Solids 280 (2001) 116-121. www.elsevier.com/locate/jnoncrysol. cited by other.

Primary Examiner: Richards; N. Drew
Assistant Examiner: Luu; An T.
Attorney, Agent or Firm: Schwegman, Lundberg & Woessner, P.A.

Claims



What is claimed is:

1. A system for providing an adaptive slew rate voltage signal to a memory cell, the system comprising: a charge pump coupled to a switch, the charge pump having a charge pump current, a charge pump load capacitance, and a charge pump voltage level, wherein the charge pump drives an output node having an output node voltage level at a first slew rate for a first voltage range; a threshold voltage detection circuit coupled to a level shifter, a delay circuit, and the output node, wherein the threshold voltage detection circuit comprises a voltage divider circuit coupled to a comparator circuit; a slew rate control circuit coupled to the delay circuit, the charge pump, and the output node; and wherein the threshold voltage detection circuit generates a detection signal when the output node voltage level reaches a predetermined threshold voltage level, the detection signal communicated to the level shifter coupled to the switch to disable the charge pump and enable the slew rate control circuit to drive the output node voltage level at a second slew rate less than the first slew rate for a second voltage range.

2. The system of claim 1 wherein the delay circuit delays the enabling of the slew rate control circuit for a predetermined delay period.

3. The system of claim 2 wherein the predetermined delay period is determined by the charge pump current and the charge pump load capacitance.

4. The system of claim 2 wherein the output node voltage level is constant during the predetermined delay period.

5. The system of claim 2 wherein the slew rate control circuit is enabled subsequent to the predetermined delay period.

6. The system of claim 2 wherein the charge pump voltage level rises to a high voltage level during the predetermined delay period.

7. The system of claim 1 wherein the predetermined threshold voltage level is a band-gap voltage level.

8. The system of claim 1 wherein the predetermined threshold voltage level is a voltage level which triggers the initiation of Fowler-Nordheim (FN) tunneling injection.

9. The system of claim 1 wherein the comparator circuit generates the detection signal when the output node voltage level equals the predetermined threshold voltage level.

10. The system of claim 1 wherein the first voltage range is between a supply voltage level to the predetermined threshold voltage level.

11. The system of claim 1 wherein the second voltage range is between the predetermined threshold voltage level to a high voltage level.

12. The system of claim 1 wherein the slew rate control circuit comprises a control signal level shifter.

13. The system of claim 1 further comprising the output node having an output load capacitance, wherein the second slew rate is independent of the output load capacitance.

14. The system of claim 1 wherein the memory cell is an Electrically Erasable Programmable Read-Only Memory (EEPROM) cell.

15. The system of claim 1 wherein the memory cell is a Flash memory cell.

16. The system of claim 1 wherein the output node voltage level is used to program the memory cell.

17. The system of claim 1 wherein the charge pump is a regulated charge pump.

18. A method for providing an adaptive slew rate voltage signal to a memory cell, the method comprising: driving an output node having an output node voltage level at a first slew rate for a first voltage range; detecting when the output node voltage level reaches a predetermined threshold voltage level; delaying driving of the output node voltage level for a predetermined delay period; and driving the output node voltage level at a second slew rate less than the first slew rate for a second voltage range subsequent to the predetermined delay period.

19. The method of claim 18 wherein the output node voltage level is constant during the predetermined delay period.

20. The method of claim 18 wherein the predetermined threshold voltage level is a band-gap voltage level.

21. The method of claim 18 wherein the predetermined threshold voltage level is a voltage level which triggers the initiation of Fowler-Nordheim (FN) tunneling injection.

22. The method of claim 18 wherein the first voltage range is between a supply voltage level to the predetermined threshold voltage level.

23. The method of claim 18 wherein the second voltage range is between the predetermined threshold voltage level to a high voltage level.

24. The method of claim 23 wherein the output node voltage level is maintained at the high voltage level subsequent to driving the output node voltage at the second slew rate.

25. The method of claim 18 further comprising the output node having an output load capacitance, wherein the second slew rate is independent of the output load capacitance.

26. The method of claim 18 wherein the output node voltage level is used to program the memory cell.

27. A machine readable storage medium having a stored set of instructions executable by a machine for providing an adaptive slew rate voltage signal to a memory cell, the instructions comprising: instructions to provide an output node voltage level at a first slew rate for a first voltage range, wherein the first voltage range is between a supply voltage level to a predetermined threshold voltage level; instructions to detect when the output node voltage level reaches the predetermined threshold voltage level; and instructions to provide the output node voltage level at a second slew rate less than the first slew rate for a second voltage range subsequent to a predetermined delay period, wherein the second voltage range is between the predetermined threshold voltage level to a high voltage level.

28. The machine readable storage medium of claim 27 wherein the predetermined threshold voltage level is a band-gap voltage level.

29. The machine readable storage medium of claim 27 wherein the predetermined threshold voltage level is a voltage level which triggers the initiation of Fowler-Nordheim (FN) tunneling injection.
Description



FIELD OF INVENTION

The present invention relates to an apparatus and method for adaptively controlling slew rates in memory devices using a regulated charge pump. In particular, the present invention relates to improving reliability and the lifespan of memory devices by selectively controlling the applied voltages and waveforms to a memory device during programming.

BACKGROUND

A memory device, such as non-volatile memory, is comprised of a plurality of memory cells. FIG. 1 is an example of a conventional memory cell 100. Memory cell 100 includes a control gate 102 in proximity to an oxide layer 104, and a floating gate 106. Fowler-Nordheim (FN) tunneling, also known as field emission, is a process used for programming memory cell 100. In FN tunneling, a high voltage level is applied to the control gate 102 via word line 108. A charge pump may be used to provide the high voltage levels to control gate 102, although any circuit that provides high voltage levels can be used, as desired.

Once the applied voltage level to control gate 102 passes a certain threshold voltage level, FN tunneling injection begins as current 113 flows from the bit line 110 through drain 112 to source 114. As current 113 flows through the floating gate 106, the drain 112 and source 114 are grounded. Concurrently, the floating gate 106 becomes negatively charged as electrons are injected and trapped in the layer. The negatively charged floating gate 106 may be interpreted as binary value 0 or 1 depending on the implementation, as desired. Since memory cell 100 is non-volatile, the cell retains its programmed state even when the applied voltage level is removed.

Memory cell reliability and the lifespan of a memory device is dependent on the high voltages and waveforms applied to the cell 100 during FN programming, in particular during FN tunneling injection. An attribute of an applied signal waveform is its slew rate. The slew rate is the maximum rate of change of a voltage signal, described by the relationship in Equation (1) as follows:

.function.dd.function. ##EQU00001## Therefore, the slew rate is the highest value derivative, or slope, of a signal waveform.

FIG. 2 illustrates an example of a conventional signal waveform 200 used for programming memory devices. From voltage level V.sub.dd 204 to V.sub.max 208, signal 200 has a constant slew rate 202. The voltage level V.sub.dd 204 is the power supply voltage. The voltage level V.sub.max 208 is a high voltage level required to change the state of memory cell 100 in FN programming. The voltage level V.sub.threshold 206 is a voltage level that triggers the initiation of FN tunneling injection and where long-term reliability of a memory cell may be compromised. The slew rate 202 of the prior art may result in unnecessary degradation of memory cells. Therefore, a need exits for improving memory cell reliability and lifespan.

SUMMARY

An apparatus and method for improving memory cell reliability is disclosed. The slew rate is reduced in an applied voltage signal used to program a memory cell when Fowler-Nordheim (FN) tunneling injection is detected. The applied programming signal is provided by a charge pump that is preferably a regulated charge pump. The charge pump is selectively controlled by a slew rate control circuit when FN tunneling injection is detected by a voltage level detection circuit at a predetermined threshold voltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein:

FIG. 1 is an example of a conventional memory cell used in a memory device;

FIG. 2 is an example of a conventional signal waveform used for programming a memory device;

FIG. 3 is an illustration of a signal waveform having an adaptive slew rate used for programming a memory device in accordance with an embodiment of the present invention;

FIG. 4 is an illustration of a regulated charge pump including slew rate control circuitry in accordance with another embodiment of the present invention;

FIG. 5 is an illustration of a threshold detection circuit in accordance with another embodiment of the present invention;

FIG. 6 is an illustration of the output of a regulated charge pump versus the output of an applied voltage signal used for programming a memory device in accordance with another embodiment of the present invention;

FIG. 7 is an illustration of a slew rate control circuit in accordance with another embodiment of the present invention; and

FIG. 8 is an illustration of a flow chart of a method for providing improved memory cell reliability during programming of a memory device in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described with reference to the drawing figures wherein like numerals represent like elements throughout. For purposes of describing the present invention, the phrase high voltage level is used. It will be appreciated that the word "high" is a relative term and not necessarily a fixed voltage. Accordingly, the phrase high voltage may be any voltage and may vary, for example, based on the processing technology and/or the material in which the memory cell is implemented. The word "level" may represent a fixed voltage or a voltage range, as desired. Memory cell 100 is used purely as an example. The present invention may be used in any memory device or memory cell. Examples of memory devices include parallel or serial Electrically Erasable Programmable Read-Only Memories (EEPROMs) and Flash memories. In addition, a node and a voltage at a node may be used interchangeably in the description forthcoming.

FIG. 3 is an illustration of a signal waveform, such as a message signal, 300 having an adaptive slew rate used for programming a memory device in accordance with an embodiment of the present invention. Signal waveform 300 may be generated by hardware or a computer program tangibly embodied in a computer-readable or machine readable storage medium containing a set of instructions for execution by a processor or a general purpose computer. From voltage level V.sub.dd 304 to V.sub.threshold 306, a first slew rate 302 is provided for programming memory cell 100 in this voltage range. V.sub.dd 304 may be a supply voltage level of 1.8 to 5.5 volts or any other voltage level, as desired. Subsequent to a delay period 312, a second slew rate 310 is utilized for the time period that the voltage increases from voltage range V.sub.threshold 306 to V.sub.max 308. The second slew rate 310 has a lower value than the first slew rate thereby reducing the negative effects that Fowler-Nordheim (FN) tunneling injection may have on a memory cell. Since the slew rate 310 is less than slew rate 302, an improved transition to V.sub.max 308 is provided and the injected tunneling current is limited thereby improving cell reliability. Memory cell reliability is improved since the reduced slew rate 310 reduces the maximum electric field applied to the oxide layer 104 during programming which reduces degradation of the oxide layer 104 and thereby improves long-term reliability and endurance of a memory cell. In addition, reliability is improved without any costly process changes.

FIG. 4 is an illustration of a regulated charge pump including slew rate control circuitry for providing signal waveform 300 in accordance with another embodiment of the present invention. In circuit 400, regulated charge pump 402 drives a voltage level V.sub.pump at charge pump output node 404. A load capacitance C.sub.pump 406 may exist at the charge pump output node 404 which is coupled to a p-type metal-oxide semiconductor (PMOS) transistor 416. Although a PMOS transistor is used in the present embodiment, any type of switch may be used. PMOS transistor 416 provides switching between regulated charge pump 402 and slew rate control circuit 422 for driving output voltage level V.sub.out at node 424. A load capacitance C.sub.out 426 may exist at the output node 424. From voltage level V.sub.dd 304 to V.sub.threshold 306, PMOS transistor 416 is ON and V.sub.out at node 424 is driven by regulated charge pump 402 and follows V.sub.pump at node 404 providing the first slew rate 302. From V.sub.threshold 306 to V.sub.max 308, PMOS transistor 416 is turned OFF and V.sub.out at node 424 is driven by slew rate control circuit 422 providing the second slew rate 310.

PMOS transistor 416 is controlled by threshold voltage detection circuit 408, which comprises a voltage divider 410 coupled to a comparator 412, and level shifter 428. The comparator 412 outputs a detection signal at node 414. The output node 414 is coupled to level shifter 428 and delay circuit 418. Voltage level V.sub.bg applied to node 411 is the band-gap reference voltage level, which may be used to define V.sub.threshold 306. The band-gap reference V.sub.bg may be dependent on the materials used to configure a memory cell.

FIG. 5 is an illustration of a threshold voltage detection circuit 500. Resistor R.sub.1 506 is coupled between nodes 524 and 510. Resistor R.sub.2 502 is coupled between nodes 510 and ground. Node 510 is coupled to the non-inverting terminal of operational amplifier (OP-AMP) 512. The inverting terminal of OP-AMP 512 is coupled to the node 511 which provides the band-gap reference voltage level V.sub.bg. V.sub.dd at node 504 provides power to OP-AMP 512. The relationship between V.sub.threshold 306, R.sub.1 506, R.sub.2 502, and V.sub.bg is given by Equation (2) as follows:

.function. ##EQU00002## The relationship between V.sub.out at node 524, voltage level V.sub.1 at node 510, R.sub.1 506, and R.sub.2 502 is given by Equation (3) as follows:

.function. ##EQU00003## When V.sub.1 510 is equal to band-gap voltage level V.sub.bg 511, i.e. V.sub.out at node 524 is equal to V.sub.threshold 306, comparator 512 switches and a detection signal at node 514 is generated.

Referring back to FIG. 4, once V.sub.threshold level 306 is detected by threshold voltage detection circuit 408 at output node 424, the detection signal at node 414 is generated and communicated to level shifter 428. The detection signal at node 414 will typically be at V.sub.dd. The level shifter 428 may be needed to raise the detection signal level from V.sub.dd to V.sub.pump in order to properly cutoff PMOS transistor 416. When voltage level V.sub.pump is provided to the gate of PMOS transistor 416 by level shifter 428, the transistor is turned OFF disconnecting V.sub.out node 424 from V.sub.pump node 404. At this point V.sub.out at node 424 will be driven by slew rate control circuit 422 which provides the second slew rate 310 and then maintains V.sub.out at V.sub.max 308. Prior to enabling the slew rate control circuit 422, a delay circuit 418 may be used.

FIG. 6 is an illustration 600 of the relationship between V.sub.out at node 424 and V.sub.pump at node 404. From voltage level V.sub.dd 604 to V.sub.threshold 606, V.sub.out follows V.sub.pump at a first slew rate 602. As stated above, at V.sub.threshold 606 node 424 is disconnected from node 404 and the delay circuit 418 provides a delay period 612. Delay period 612 allows V.sub.pump at node 404 to rise to V.sub.max 608 at a second slew rate 614. The second slew rate 614 is a result of a change in the equivalent capacitance seen at the output of the regulated charge pump 402 when PMOS switch 416 is disconnected. The delay period 612 may be determined using values for C.sub.pump 406, V.sub.max 308, V.sub.theshold 306, and I.sub.pump by Equation (4) as follows:

.function. ##EQU00004## In Equation (4), I.sub.pump is the charge pump current at node 404.

During the delay period 612, V.sub.out at node 424 remains stable at a constant value and is not driven by either the regulated charge pump 402 or the slew rate control circuit 422. After the delay period 612, delay circuit 418 provides a control signal 420 to enable slew rate control circuit 422 at which point V.sub.out at node 424 is driven by slew rate control circuit 422 at a third slew rate 610, which is less than the first slew rate 602 and second slew rate 614, until V.sub.max 608 is reached.

FIG. 7 is an illustration of a slew rate control circuit 700 in accordance with another embodiment of the present invention. Control signal (Ctrl) 702 is provided to level shifter 704 which raises the level of control signal 702 from V.sub.dd 304, or high, to V.sub.pump at node 708 resulting in control high voltage signal (Ctrlhv) at node 706. If the Ctrl 702 is low, such as at a ground value, then Ctrlhv is low and PMOS transistor 710 is ON. Correspondingly, when Ctrlhv is low, n-type metal-oxide semiconductor (NMOS) transistor 712 is OFF. Since the gate of PMOS transistor 722, which acts as an amplifier, is driven by V.sub.pump at node 708 via PMOS transistor 710, PMOS transistor 722 is OFF resulting in no connection between nodes 708 and 724 when Ctrlhv is low. In this case, V.sub.out at node 424 is driven by regulated charge pump 402.

When Ctrl signal 702 is set to high, or V.sub.dd, Ctrlhv 706 is raised from V.sub.dd to V.sub.pump at node 708 by level shifter 704. When Ctrlhv 706 is set to V.sub.pump, PMOS transistor 710 is OFF and NMOS transistor 712 is ON resulting in current I.sub.ref 716 which is controlled by reference voltage level V.sub.ref to the gate of NMOS transistor 714. When NMOS transistor 712 is ON, the voltage level of node 718 gate voltage G.sub.p2 decreases turning PMOS transistor 722 ON. When PMOS transistor 722 starts conducting current I.sub.p 728, V.sub.out at node 724 begins to rise at a certain slew rate. Due to the coupling feedback capacitance C.sub.ref 720 between nodes 718 and 724, a positive variation from the output is provided to gate voltage G.sub.p2 which counteracts the negative variation on to G.sub.p2 due to I.sub.ref 716. These two counteracting effects on the voltage G.sub.p2 at node 718 provided by the feedback path on PMOS transistor 722 results in a stable, balanced, equilibrium node voltage at 718.

Stilling referring to FIG. 7, since the gate voltage G.sub.p2 is held constant, the relationship between the pump current I.sub.p 728 and reference current I.sub.ref716 is given by Equation (5) as follows:

.times..function. ##EQU00005## The slew rate of the output voltage V.sub.out at node 724 is given by Equation (6) as follows:

.function. ##EQU00006## Substituting Equation (5) into Equation (6) for I.sub.p 728, Equation (7) is given as follows:

.function. ##EQU00007## Equation (7) shows that the slew rate of V.sub.out at node 724 is independent of the output capacitance C.sub.out 726 and the slew rate may be adjusted using different values for I.sub.ref 716 and C.sub.ref 720, as desired. I.sub.ref 716 may be adjusted by changing the level of V.sub.ref. It is favorable to have the slew rate independent of C.sub.out 726, since it provides a more controlled and stable slew rate. Without the slew rate control circuit 422, at high voltages the slew rate of V.sub.out at node 424 would be highly dependent on the C.sub.pump capacitance 406 and the current driving ability of regulated charge pump 402. As a consequence, large variations of C.sub.pump 406 can result in slew rate variations, which are undesirable when programming memory, especially during FN tunneling injection. For instance, C.sub.pump 406 may vary when programming a memory device using a plurality of bits in parallel since the equivalent capacitance, or the total capacitive load, seen by C.sub.pump 406 may vary. Table 1 shows the independence on the slew rate by varying values of C.sub.out 726 using circuits 400 and 700 of the present invention.

TABLE-US-00001 TABLE 1 Slew Rate (in Volts per C.sub.out (in picofarads pF) microsecond V/.mu.s) 10 0.48 20 0.48 40 0.47 60 0.47 80 0.46 100 0.455

FIG. 8 is an illustration of a flow chart 800 of a method for providing the controlled slew rate 300 comprising of steps 810 to 890. In step 820, regulated charge pump 402 drives V.sub.out at node 424 from V.sub.dd 304 to V.sub.threshold 306 at a first slew rate 302. In steps 830 and 840, threshold voltage detection circuit 408 monitors V.sub.out 424 until it reaches V.sub.threshold level 306. In step 850, threshold voltage detection circuit 408 disables regulated charge pump 402 when V.sub.out 424 reaches V.sub.threshold level 306 by communicating a detection signal on node 414 to level shifter 428 which turns OFF PMOS switch 416. In step 860, delay circuit 418 delays enabling of the slew rate control circuit 422 for a predetermined delay period 312 while V.sub.out 424 stays at a constant value and V.sub.pump at node 404 rises to V.sub.max 308. In step 870, after delay period 312, slew rate control circuit 422 is enabled and V.sub.out at node 424 rises at a second reduced slew rate 310 until it reaches V.sub.max 308. In step 880, slew rate control circuit 422 maintains V.sub.out at node 424 at V.sub.pump, which is substantially equal to V.sub.max 308 at this point.

Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. The present invention may be implemented in a computer program tangibly embodied in a computer-readable storage medium for execution by a processor or a general purpose computer for use with or by any non-volatile memory device. Suitable processors include, by way of example, both general and special purpose processors. Typically, a processor will receive instructions and data from a ROM, a random access memory (RAM), and/or a storage device. Storage devices suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). Types of hardware components or processors which may be used by or in conjunction with the present invention include Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), microprocessors, or any integrated circuit.

*


Free Web Sudoku Puzzles.
Solve with your browser.
  4   1   9     7
          2      
3 9   5 8       6
4 5             1
  7 3       2 8  
9             6 3
5       7 6   9 8
      9          
6     2   1   4  
What is it?



Add Your Site · Terms Of Service · Privacy Policy


DISCLAIMER
Linkgrinder is a free service that searches the Internet and indexes all files found so that you may search quickly and easily for shared files. These files are created and made available individually by users whose identity we are not aware of and who we have no control over. In essence we function like a search engine tool; these files ARE NOT STORED OR SERVED BY OUR NETWORK. We are not responsible for any materials obtained by using our service. We do not monitor any of the contents of these files. These files may contain viruses, illegal materials, materials inappropriate for minors, offensive files and the like. BY USING OUR SERVICE, YOU ASSUME FULL RESPONSIBILITY FOR DOWNLOADING THESE MATERIALS AND WILL INDEMNIFY US FOR ANY DAMAGES THAT MAY BE INCURRED.

For More Specific Information VIEW OUR TERMS OF SERVICE.

Thank you and Enjoy!