Can't we directly connect the bias circuit to the gate of inverter? What advantage we get by using this resistor R?
The two bottoms N-MOSFET are working as a current mirror, R does not interfere with RF signal, thus defines DC operating point. However, RC is the time constant and it should be more than 1/f.
This is a crude circuit. I mean, that seems a rather uncommon way of making an amplifier.
Anyway,
- The NMOS-PMOS pair at the right provides the refererence. Ie, there is a certain current
flowing though this, and then the next 2 NMOS/PMOS pairs are baised to have the same current.
- In the first stage, the signal is fed to the PMOS. I would assume the DC point of the PMOS
is also controlled, but this is not shown.
- The function of the resistor is to put the input voltage (for DC) for the second NMOS/PMOS
pair identical to the reference (the right pair).The signal is coupled via the capacitor.
- For sure you cannot remove the resistor. If you do, the impedance on the gate becomes low
(due to the right 'reference' circuit), and it cannot amplify the signal coupled via the capacitor
any more.
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