Preliminary stuff

Prof. Paul Hasler

Capacitor Circuits

Vout(t)GND

C2

QI

Capacitor Circuits

Vout(t)GND

C2

QdVout(t)

dtC2 = - Iin

I

dQ(t)

dt = Iin

We get an integration….

Capacitor Circuits

Vout(t)GND

C2

QdVout(t)

dtC2 = - Iin

Vout(t) = Vstart - t C2

Iin

I

dQ(t)

dt = Iin

We get an integration….

For constant I, we get

Capacitor Circuits

Vout(t)GND

C2

QdVout(t)

dtC2 = - Iin

Vout(t) = Vstart - t C2

Iin

I

dQ(t)

dt = Iin

We get an integration….

For constant I, we get

t

Vout(t)

Capacitor Circuits

Vdd

C

Vd

Vref

Vout

Vtun

t

Vout(t)

Injection

Tunneling

Floating-Gate Systems

Prof. Paul Hasler

Floating-Gate Devices

• Information Storage

• Floating-Gate Transistor

• Modifying Floating-Gate Charge- UV photo-injection- Electron tunneling- Hot-electron injection

• Digital Memory (EEPROMs)• Analog Memory• Floating-Gate Circuits• Floating-Gate Systems• Floating-Gate Adaptation

All of this in a standardCMOS process

Floating-Gate Circuits

• Decrease Floating-Gate charge by hot-electron injection

• Increase Floating-Gate charge by electron tunneling

Capacitor-Based Circuits

• Resistors and Inductors define the circuit dynamics

• Capacitors are the natural elements on silicon ICs

Charge Modification

Electron Tunneling

Increasing the applied voltage decreases the effective barrier width

The range of tunneling currents span many orders of magnitude.

(oxide voltage)-1

pFET Hot-Electron Injection

The injected electrons are generated by hole impact ionizations.

**Injection current is proportional to source current, and is an exponential function of

dc.

Vinj = 430mV

Offset elimination

-3 0 3-80

0

Differential Input Voltage

Diff

eren

tial O

utpu

t Cur

rent

(nA

)

Direction of offset due to hot-electron injection ontothe floating gate devices.

80

Small Linear Range

Huge Linear Range

Offset is less than 1 mV.

Tunable Voltage Sources

SELECT UP DOWN

VOLTMETER

Cf

Vref

TunnelingCircuitry

Inject

Select

TunnelSelect

InjectionCircuitry

Output Voltage: (if selected)

• Decreased by Tunneling

• Increased by Injection

Arrays of Prog.Voltage Sources•EPot elements are arranged in a linear array with a shift register selecting one element at a time

E Vout

tunnel

inject

select

E Vout

tunnel

inject

select

E Vout

tunnel

inject

selectSpeed used: ~1V/ms ( range is 100V/ms to very very slow)

Translinear Element using Floating-Gate Devices

GND GND GND

Iout

I1 I2

VddVdd

A Single-Ended Gm-C filter using Floating-Gate Devices

GND GND

I1 I2

VddVdd

-1

C

C

C

Vout

Vin

C

0 50 100 150 200 250 300 350 400

0.1

1

10

100

Half-second pulse steps

Selected Synapse

Non-selected Synapse

Injection PhaseTunneling Phase

Programming / Selectivity in FG Array

V1 V2 V3 V4

• channel current (Gate voltage)•Large Source to drain voltage (high field for hot electrons)

2 conditions for injection

Programming a Floating-gate Device

• Tunneling– Remove charge from floating-

gate– Less control per device– Used as “global” erase– Decrease current for a given

threshold

• Hot-electron injection– Add electrons to the floating-

gate– Isolate devices well– Program accurately– Increase current for a given

gate voltage

Vtun

Vin

+

I

+

Basic Programming StructureV1 V2 V3 V4

Injection Gate: Column isolation Source-Drain: Row isolation

Both: Device isolation

Programming a FGV

tun

Vin

+

A

+-

Offchip

Bring chip up to program voltageBring drain up to match Vds(run)Set Gate volt to read currentRead Current through deviceCalculate next pulse on drainPulse Drain voltageRinse and repeat

Basic Programming Structure

DECODERGate Pin

Column

S

S

S

SSSS

S

S

S SS

Input Signals / Circuitry

(M. Kucic, P. Smith, P. Hasler, 2000-2001)

Programming Board Interface

AdditionalUser

Circuits

ToDrain

CurrentMonitorBlock

DAC

SPI

Regu lator

ToGate

LevelShifters

Selection Logic

Programmin g Board Testing Board

Programming Board, v0.1

Answers to Typical Questions

Is storing analog charge levels on a floating-gate reliable?Yes, we have seen little to no movement over months (like 0.01mV in EPots)

Isn’t floating-gate programming is slow?We are currently programming in ms times, should get to 1-10s times as in EEPROM, and the process can operate in parallel.

Does this require specialized processes?Can be built in either Double Poly or Single Poly (i.e. digital) processes

Automatic Floating-Gate Programming

0 10 20 30 40 50 60 700

2

4

6

8

10

12

Flo

atin

g-G

ate

Bia

s C

urr

en

t (n

A)

Position along the Array

cosine

-cosine

Measure Current

< target

Compute Drain V

Yes No

Inject Element

Select Next ElementSTART Get in Range

Programming ResultsProgramming Algorithm

(NSF ITR)

Array Programming

V

VtunVtun

M1 M2Vfg1 Vfg2

I-I+

Vg2

Vd2

To Circuit

To Circuit

Applications of Floating-Gate Circuits in Systems

• Programmable Filters / Adaptive Filters

• Auditory / Accoustical Signal Processing

• Image Processing

• ADCs, DACs, etc.

Single-Transistor pFET Synapses

1. Store a weight value2. Input x stored W3. dW/dt = correlation of the f( input , a given error signal)

Vdd

Vtun1

C1

M1

M2Vb

Vg

VdProgrammable and Adaptive Analog Processing

(NSF CAREER)

Fourier-Based Programmable Filters

Bandpass Filters, Exp Spaced (Hard in DSP)

Vin

W11 W12 W13 W14 W15 W1n

W21 W22 W23 W24 W25 W2n

Iout1

Iout2

FG tuning of bandpass filters as well as coefficients…

(M. Kucic, P. Hasler, et. al. 1999-2001)

Analog Speech Front-End Blocks

Analog HMM ClassifierVQ Classifier

Analog Cepstrum

Outputs

Cepstrum

VQ

HM

M

Microphone

Digital S

ignalProcessing

Transform Imager

Image Elements

Floating-GateElement

AnalogComputing

Array

Transformed Output Image

Ti m

e ba

s is

1

Ti m

e ba

s is

2T

i me

bas i

s 3

Ti m

e ba

s is

4

Ti m

e ba

sis

m

Imag

e Se

nsor

Iout

Vin

Basis Functions

Dig

ital

Con

trol

Our approach allows for

• Bio-inspired (Retina)

computation

• A programmable

architecture

• High-fill factor (~50%)

pixels like

CMOS imagers.

Can build in other neuromorphic designs into this structure

Layout of Imager Cell

30 = 9m

39

= 1

1.7

m

• Fill Factor ~ 50%

• Fabricated in 0.5m CMOS

0.5m 0.25m

Photo 8mx6m 3.2mx2.4m

Array 128 x 128 512 x 512 (Size) (1.72mm2) (4.4mm2)

Adaptive Floating-Gate Circuits• Full range of floating-gate circuits abilities• Continuously programming (tunneling / injecting) therefore, circuits at a slower timescale

Fundamental operation for adaptive systems: Adaptive Filters, Neural Networks, Neuromorphic Models of Learning

Equilibrium point: Tunneling current = Injection current

AFGA Behavior

0 2 4 6 8 10 12 14 161.5

2

2.5

3

3.5

4

4.5

Input voltage (V)

Out

put v

olta

ge (

V)

Sine Wave + Voltage Step Input

Voltage Step InputV

Vout

Vdd

C1

Vin

Vtun1

Vfg

Autozeroing Floating-Gate Amplifier (AFGA)

Adaptive Diff-Pair

V1

Vtun

V2

Vtun

Vdd

Vdd

VCM

V

Vout1 Vout2

I1 I2

Common Mode Feedback

Vn

Can be directly extended to:• Multipliers / Mixers• “Bump” Circuits

Translinear Element using Floating-Gate Devices

GND GND

Iout

Iin

Vdd

C

CV1

V2