I want to design a simple constant Gm bias circuit in order to provide a voltage supply to the main circuit
but how can I start to design such a circuit?
and what's the main advantage of this constant Gm bias circuit? Is it not variant to the process and temperature variations?
yeah constant Gm circuit , mean that the Gm of the transistor will be constant against temperature and process variation but this circuit need external resistor so the Gm will depend on this resistor it shoud be 1% tolerance
So what's the main advantage of such Gm constant circuit?
Is is more robust to the process and temperature variations compared with the simple resistor and MOSFET biasing
yeah constant Gm circuit , mean that the Gm of the transistor will be constant against temperature and process variation but this circuit need external resistor so the Gm will depend on this resistor it shoud be 1% tolerance
The idea of constant gm bias circuit is to generate bias current(Iref) which is the function of a resistor and inversely proportional to µCox(W/L); then if you pass this current into a transistor whose gm equals sqrt(2*µCox(W/L)*Iref). You can see that the only variable left is the resistor( plus some constant factor).
I want to design a simple constant Gm bias circuit in order to provide a voltage supply to the main circuit
but how can I start to design such a circuit?
and what's the main advantage of this constant Gm bias circuit? Is it not variant to the process and temperature variations?
constant-gm is PTAT current, based on a constant R.
So, if the R is change with temperature, the GM will not constant.
Added after 1 minutes:
katrin said:
I want to design a simple constant Gm bias circuit in order to provide a voltage supply to the main circuit
but how can I start to design such a circuit?
and what's the main advantage of this constant Gm bias circuit? Is it not variant to the process and temperature variations?
Constant gm bias circuits are generally supply independent circuits.Circuit consists resister R (which basically defines the module current) which is process and temp dependent. Due to that module current is supply independent but not process and temperature. You can get the further detail in 11th Chapter of Razavi.
This circuit is used in most of the designs (opamps,current mirrors,comparators etc) for biasing.
gm is determined by geometric ratio only. It is independent of power supply voltage, process parameter, and temperature. This is only true to the first order of approximation, since the body effect is neglected. In addition all other transconductance are also stabilized since all transistor currents are derived from the same biasing network.