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EE6307 CA1: Continuous-Time Filters

Semester 2, 2022-2023

1.   Using large-signal saturation model equation of MOSFET to derive the large-signal output current expression of Fig. 1. The transconductance parameters for M1  and M2 are k1  = and for M3  and M4  are k2  = respectively.  State your assumptions.

Figure 1

Draw and explain the improved transconductor that can further enhance the input signal handling capability.

2.   Design  a  MOSFET-C  fully-balanced  filter  based  on  the  continuous-time  filter prototype as shown in Fig. 1. Determine the unknown component values in the filter prototype at nominal cut-off frequency. In the MOSFET-C  filter design, find the tuning range of the control signal on the MOSFET-C filter and all the channel lengths for MOSFET resistors. State the assumptions. The specifications of the MOSFET-C filter are given as follows:

• Low-pass Butterworth response

•   Q= 0.707, DC gain H0 = 0 dB

•   C1 = C2 = 20 pF

•   Channel width of MOSFET devices = 5m

•   Tuning range  +/-  25%  from nominal, with minimum  200mV  for  over-design margin for control voltage VC

•   Cut-off Frequency fo = 10 kHz

•   Maximum Signal = 200 mVpeak

•   Supply = +/- 5V

•   All p-channel devices

It is given that the p-channel MOS transistor process parameters are as follows

μpCox = 30 μA/V2

Vtp = -0.9 V

γ = 0.5 V1/2

Cox = 1.9 x 10-3 pF / (μm)2

20F = 0.7V

Figure 2