0.8V Bulk-Driven Variable Gain Amplifier

1. 0.8V Bulk-Driven Variable Gain Amplifier George Raikos and SpyridonVlassis Electronics Laboratory Physics Department University of Patras http://www.ellab.physics.upatras.gr

2. Introduction • Utilizes : • Bulk-driven transistors low-voltage operation • Master-slave technique control voltage gain duplicate the gain slope • Based on pseudo exponential approximation function (1+x)/(1-x)≈exp(2x)  linear in dB gain. Electronics Laboratory, Physics Dept. ICECS 2010

3. Principle of operation • Bulk transconductance of a MOS transistor is : • If ID-input=1+x and ID-load=1-x then :

4. Principle of operation • We seek to make:

5. Gain Control Circuit • Generates the appropriate currents for exponential circuit  controls the VGA. • Based on master-slave technique. Electronics Laboratory, Physics Dept. ICECS 2010

6. Gain Control Circuit • IR=gmb1VR • VR relatively small (50mV) • VCM:Common mode voltage • VFb the feedback voltage • Thus, IR=IB+IT Electronics Laboratory, Physics Dept. ICECS 2010

7. Gain Control Circuit • The input transconductance is equal to: Linear dependence from tuning current gmb-input≈(IB+IT)/VR Process independence • The slave pair obtain equal transconductance with master pair. gmb-input,slave≈(IB+IT)/VR Electronics Laboratory, Physics Dept. ICECS 2010

8. Variable Gain Amplifier • Bulk-driven differential pair with bulk diode-connected loads • Gain control circuits • The two gain control circuits produce the appropriate currents that bias and control the gain of the VGA. Electronics Laboratory, Physics Dept. ICECS 2010

9. Variable Gain Amplifier • Thus: • the gmb-input equals to (IB+IT)/VR • the gmb-loads equals to (IB-IT)/VR • Amp1 stabilize output common-mode voltage •  produce the diode loads bias current Electronics Laboratory, Physics Dept. ICECS 2010

10. Variable Gain Amplifier • Voltage gain: • where x=IT/IB Electronics Laboratory, Physics Dept. ICECS 2010

11. Simulations Results • Technology : Standard 0.18um CMOS • VDD=0.8V • IB=10uA/15uA/20uA • IT=50% of IB

12. Simulations Results • Gain range of the proposed and the conventional VGA approach against tuning current IT • Linearity error versus tuning current IT with bias current IB as a parameter (10uA, 15uA & 20uA). Electronics Laboratory, Physics Dept. ICECS 2010

13. Simulation Results • Gain variation of VGA versus tuning variable IT with bias current IB as parameter (10uA, 15uA & 20uA) Electronics Laboratory, Physics Dept. ICECS 2010

14. Simulations Results

15. Conclusions • A low-voltage VGA was introduced. • Based on master-slave technique • Utilizes bulk-driven PMOS input transistors • Implements the pseudo exponential approximation function : Electronics Laboratory, Physics Dept. ICECS 2010

16. Conclusions • Benefits of the proposed VGA topology : • a linear-in-dB gain range almost equal to 17dB • linear gain tunability • less than ±0.5dB linear error • stability over process • a doubled slope of gain curve Electronics Laboratory, Physics Dept. ICECS 2010

17. Thank You For your Attention!!!