Design of Operational Transconductance Amplifierer based Multiplier

Design of Operational Transconductance Amplifierer based Multiplier

Neha Niharika Swatantra Kumar

HMR Institute of Tecnology Sharda University

Electrical & Electronics Department Electronics and Communication Department

Delhi Greater Noida, India

Abstract- In recent years interests have been seen in wireless system and software radio using sigma-delta modulators to digitize signals near the front end of radio receivers. Such applications necessitate clocking the modulators at a high frequency (MHz or above). A continuous-time implementation using transconductors and integrators rather than discrete time implementation using switched capacitors is preferred for high frequency operation. OTA based multiplier containing two OTAs and transistor connected diode is based on 0.3µm pwell CMOS technology simulated using Pspice software.

1. INTRODUCTION

   The OTA is a programmable device and has only a single high-impedance node, in contrast to conventional op amps. This makes the OTA an excellent device candidate for high- frequency and voltage (or current) programmable analog basic building blocks.The applicability of OTA based multiplier as components in the design of linear networks has been extensively discussed. The multiplier has gigahertz frequency response is suitable to use in communication system. Excellent contributions are reported of OTA based multiplier dealing with particular important nonlinear problems. In this paper, rather than try to tackle a specific problem, we focus our attention on a general approach dealing with multiplier. Nothing special is done to optimize the circuit performance but rather to explore the potential and applicability of the OTA-based Multiplier in communication systems.

2. OTA BASED MULTIPLIER DESIGN

   A two-input four-quadrant multiplier has an output current given by

   I 0 = Km V1 V2 (1)

   where the multiplier constant Km has units of amperes per square volt.

   If V1 and V2 can take any positive or negative sign, the multiplier is called a four-quadrant multiplier.

   shown in Fig. 1(b) and 1(c).The triangular block labeled a represents a signal attenuation (with an attenuation factor a); its function is to equalize the maximum voltage swing of V1 and V2..

   V BIAS is the usual-bias control of the OTA The two options of Fig. 1(b) and Fig. 1(c) allow us to change the sign of Km . Thus for the circuit of Fig. 1(b) we obtain

   I01 = gm1 V1 = K(VI1 +VSST ) V1 (2)

   I02 = – gm2 V1 = – K(V I2 +V SST) (3)

   Where K is a process and geometry dependent constant, VSST = VSS Vt , and Vt is a transistor threshold voltage V1

   I0

   V2

   KM

   (a) + I01

   –

   VI2

   V1 a I0

   -VBIAS

   –

   + I02

   VI1

   This OTA based multiplier is represented in Fig.1(a). The corresponding OTA-based implementations are

   V2 a

   -VBIAS

   (b) Therefore, we can make the sign of KM positive or negative.

   M22

   M3 M5

   M6 M10

   M12

   M2SJ102 V9

   + I01

   M2SJ102 M23

   M24

   M2SJ102

   M2SJ102 M2SMJ21S0J2102 M9

   M11

   M21 5v

   M2SJ102

   M2SJ102 M13 0

   – M2SJ102

   M1

   M2 M4

   M2SJ102

   M7 M8

   M14 M15

   M2SJ102

   M2SJ102

   M2N6659 M2N665M92N6659 M2N6659M2N6659 M2N6659M2N6659

   0

   M16

   M17

   V1 V2

   I0

   -VBIAS

   M80

   M81

   M78

   M2N6659 M79

   M76

   M2N6659 M77

   M74

   M2N6659 M75

   M2SJ102 M19

   M2SJ102

   M2SJ102 M18

   M2SJ102

   0 V13

   2vdc

   0

   M2N6659

   M2N6659

   M2N6659 V10

   5v

   0

   V R5

   1k

   – I02

   +

   M41

   M47

   M42

   M48

   M43

   M49

   M44

   M50

   M45

   M51

   M46

   M52

   0

   V11

   5v

   0

   M53 M54

   M55

   M56

   M57

   M58

   M59

   a

   (c)

   -VBIAS

   R1

   V4 V 1k

   VOFF = 0v

   VAMPL = 2 FREQ = 1KHZ

   VOFF = 0V VAMPL = 1 FREQ = 1KHz

   R2 R3V

   1k 1k

   V21

   0

   V

   M88

   M89

   V18

   M86

   M87

   M84

   M85

   M82

   M83

   0

   M93

   M25

   M2N6659 M20

   M2N6659 M91

   V16

   5v

   Fig. Multiplier: (a) symbol, (b) OTA implementation 1, and (c) OTA implementation 2, 0< a <1.

   V I1 = a0 V BIAS = – V BIAS (3a)

   V I2 = aV 2 V BIAS (3b)

   The output current,

   I 0 = I 01 + I 02 , (3c)

   Put the values of I 01 and I 02 , in equation 3(c). Thus the output current becomes

   I 0 = [K(-V BIAS + V SST ) K(a V 2 V BIAS + V SST ) )] V 1

   Or

   I 0 = a K V1 V2 = K M V1 V 2 , (4) K M = a K

   A similar analysis of the circuit of Fig. 1(c) gives I 0 = – a K V1 V2 , K M = – a K

   2vdc 0

   0 0

   Fig.4 Internal circuit diagram of OTA Based multiplier.

3. EXPERIMENTAL RESULTS OF OTA MULTIPLIER

The structure used is as shown in Fig. 4. The measured value of KM is 3.3 pA/V2. The output current was measured across a 100-k load resistor.

The nonlinearity error is shown in Fig. 5 For V2 is 2V signal is applied, while keeping V1 equal to 1 V.

Fig. 6 shows the multiplier being used as a modulator where both input signals are sinusoidal.

1V. CONCLUSION

A Multiplier based on OTA is proposed. The multiplier has gigahertz frequency response is suitable to use in communication system for high frequency applications. The circuit is based on 3.0 m pwell CMOS technology simulated using PSPICE software.

This technique provides; wide dynamic range, MHz- bandwidth response and low power consumption. The proposed circuit has been simulated with PSPICE software. The primary application for an OTA is however to drive low-impedance sinks such as coaxial cable with low distortion at high bandwidth. Hence, improved OTA such as the MAX436 has optimized.

REFERENCES

Fig.5 Nonlinearity multiplier error: fixed V2=1 V and variable VI.

Fig. 6 Multiplier as modulator

1. Edgar Sanchez Sinencio, seniormember, IEEE, Jaime, Ramirez

   Angulo, member, IEEE, Bernabe linares-barranco, Andangel Rodriguez-Vazquez, member. A tutorial IEEE circuits

2. A Textbook of Operational Transconductance Amplifier and Analog Integrated Circuits Paperback Import, 13 May 2010 by Tahira Parveen (Author)

3. http://www.itervis.com/simulation-and-layout-design-of-ota- amplifier/

4. R. L. Geiger and E. Sánchez-Sinencio, "Active Filter Design Using Operational Trans conductance Amplifiers: A Tutorial," IEEE Circuits and Devices Magazine, Vol. 1, pp.20-32, March 1985.

5. https://en.wikipedia.org/wiki/Operational_transconductance_ampl ifier.