Done By: Raza Hanif (3336928)

Raheel Choudhary

Fawad Usman Rathore

Contents of Presentationo Background and literature review

o Different applications of CMOS OpAmp

o Choice of complex electronic system

o proposed circuit (cmos opamp) to be implemented in the system -> In the Book

o analysis of proposed circuit

o Improved, and more complex circuit

o Analysis

o System Analysis

o Conclusion

BackGround Complementary Metal-Oxide-Semiconductor (CMOS) technology is circuit implementation using both pMOS and nMOS transistors on the same silicon chip.

CMOS designs typically offer high gain and speed at low power consumption.

CMOS scales well to smaller devices without drastic changes in performance.

This device is commonly used to amplify small signals, to add/subtract voltages, and in active filtering.

It must have high gain, low current draw, and should function over a variety of frequencies.

In Context with Textbook

OP741

TTL L

OG

IC

Why CMOS over TTL?

MOSFETS consume less power in the driver circuit. MOSFETS have greater bandwidth.

MOSFETS are thermally more stable.

MOSFETS are considerably ‘faster’ than BJT’s.

CMOS ICs use much less power than TTL

Analysis of a Complex Electronic System

The input consists of differential electrode inputs and the outputs are from: an amplifier, a peak detector, a trough detector, and a level detector.

A trough is a noticeable decline in the signal strength

Implication of CMOS (OTA) amplifier in neural amplifier

There is a great demand for technologies that enable neuroscientists and clinicians to observe the simultaneous activity of large numbers of neurons in the brain.

While there are microelectronic devices being developed for small-scale amplification of the weak bioelectrical signals, existing circuits typically have unacceptable noise levels or consume too much power to be fully implanted in large quantities.

In our electronic system, the bioamplifier must dissipate little power so that surrounding tissues are not damaged by heating. A heat flux of only 80 mW/cm2 can cause necrosis in muscle tissue.

Necrosis: accidental death of cells and living tissue.

In small chronic impants, the power dissipation should not exceed a few hundred miliwatts.

Design and testing of a fully integrated amplifier suitable for recording biological signals from the millihertz range to 7 kHz.

Design such that the amplifier offers the best power – noise tradeoff.

Main Objective

Operational Transconductance Amplifier (OTA)

Pg. 885 in textbook

Operational Transconductance Amplifier (OTA)

The input voltage controls an output current by means of the device transconductance, labeled gm.

What is important and useful about the OTA’s transconductance parameter is that it is controlled by an external current, the amplifier bias current, IABC , so that one obtains

From this externally controlled transconductance, the output current as a function of the applied voltage difference between the two input pins, labeled v+ and v-, is given by

Analysis of OTA Circuit

Power dissipation in the circuit is acceptable, but it is still not close to 1 mW, which is ideal for biosignal amplifiers.

Possible Solutions:

I) Either, try to improve this circuitII) Come up with another circuit that can supply high enough open loop gain, with low power dissipation.

One possible design for a Low power CMOS Operational Amplifier

CL2p

VSS

Vo

VDDVOS

Vin

OUT

+

-

V+V-

AC Analysis of the amplifier

DC

Gain

of th

is c ircuit is a

bou

t 145

dB

75

2

7642

62

6)()(

)76()42(

2

)()(DD

np

dsdsdsds

mm

IIL

W

L

Wkk

gggg

gg

vi

vo

OUT

+

-

V+V-

VSS

Vo

VDDVOS

Vin

CL2pPower Dissipation of the

amplifier

The circuit dissipates only about 180 uW of power, which is quiet low compared to the circuit analyzed before

(ID1 + ID2 + ID3)*(VDD-VSS)

Result on the Oscilloscope

Transient Response of the Circuit

Time domain response of the circuit when it is excited with a sinusoidal signal.

OUT

+

-

V+

V-

RF2

1M

Vout

Vin

VSS

CL2p

VDD

RF110M

Closed Loop Circuit with Rf & Rs in inverting configuration

Result on the Oscilloscope

Q1

JFET_P_VIRTUAL

Q2

JFET_P_VIRTUAL

Q3

JFET_P_VIRTUAL

Q4

JFET_P_VIRTUAL

Q5

JFET_N_VIRTUAL

Q6

JFET_N_VIRTUAL

VDD5V

Q7

JFET_N_VIRTUAL

Q8

JFET_N_VIRTUAL

Ibias100uA

VSS-5V

Q9

JFET_P_VIRTUAL

Q10

JFET_P_VIRTUAL

Q11

JFET_N_VIRTUAL

Q12

JFET_N_VIRTUAL

Q13

JFET_P_VIRTUAL

Q14

JFET_P_VIRTUAL

Q15

JFET_N_VIRTUAL

Q16

JFET_N_VIRTUAL

Q17

JFET_P_VIRTUAL

Q18

JFET_P_VIRTUAL

Q19

JFET_N_VIRTUAL

C1

15pF

Q20

JFET_N_VIRTUAL

Q21

JFET_P_VIRTUAL

Q22

JFET_N_VIRTUAL

Q23

JFET_P_VIRTUAL

C2

15pF

V1

1 V 1kHz 0Deg

Many other design possibilities

Conclusion

The design process that was followed resulted in a CMOS operational amplifier design that at least met and, in a few cases, exceeded the design objectives by a large margin. The notable performance areas were the DC open loop gain of 145 dB, and the power consumption of 180 uW. Also, the settling time was quite low as can be seen by the transient response of the circuit, which means the circuit is relatively ‘fast’.

A great deal was learned in the design process, including how to approach a design project, the tradeoffs involved in a CMOS op-amp design, patience, and how to stay up late.

There could still be a lot improved in this circuit, but requires knowledge that is beyond the scope of this course, mainly in the field of VLSI.

References

R. R. Harrison and C. Charles, "A low-power low-noise CMOS amplifier for neural recording applications," IEEE J. Solid-State Circuits, vol. 38, pp. 958-965, 2003.

Yiqin Chen, Mark E. Schlarmann and Randall L. Geiger, "An Improved design Formulation for design and Optimization of Operational Amplifiers," MWSCAS’99 The 43rd Midwest Symposium on Circuits and Systems, New Mexico, USA, 8-11 August, 1999.

Electrophysiology, From: [http://en.wikipedia.org/wiki/Electrophysiology]. Retrieved on November 10th, 2006.