YDO Vout CMOSN Figure 2.

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Ydo Vout Cmosn Figure 2 1 (59.41 KiB) Viewed 60 times

In order to significantly increase the output resistance seen by
the load, the current source was modified as shown in Figure 2:
resistor Rs =10 kOhm was added between the MOSFET
source terminal and ground.
Bias voltage VGS was adjusted accordingly to keep the same drain
current value of 200 uA.
Find the required bias voltage VGS (in
Volts) for the circuit in Figure 2.
Estimate the output resistance of the current source
in kOhm (Figure 2) seen by the resistive load.
Imagine an AC probe current source (say,
Iprobe = 1uA AC) inserted between
the resistive load and and the drain terminal of NMOS
transistor and find the corresponding AC output voltage at the
drain of the MOSFET it creates.
Rout = Vout/Iprobe.
Note that gate current is zero therefore the AC currents into
the drain and out of the source terminals have the same value of
1 uA. That source current creates AC voltage drop
across Rs which is AC gate-to-source voltage. This
VGS is amplified by NMOS transistor. The output AC
voltage at the drain of the MOSFET, and Rout of the
current source, respectively, will be very
high.
Estimate the minimum output voltage of the current source in
Figure 2: Vout_min in Volts.
YDO Vout CMOSN Figure 2.