promach
Advanced Member level 4
What do you guys think about the following gyrator circuit ?
Someone told me the following:
Anyone up for a discussion regarding the mosfet sizing ?
Someone told me the following:
Let's put a voltage on v(in) and see the current drawn by that voltage. The inverter is high impedance, so none goes into that, so it will be just the current out of the diff pair. At DC, We get a current out of the inverter Iinv = Gm1*V(in). That current is multiplied by the output resistance of the inverter Ro,inv to give V(b) = V(in)*Gm1*Ro,inv. Then we multiply by the diff pair Gm2, so Iout = Gm2*V(b) = V(in)*Gm2*Gm1*Ro,inv. Rtest = Vin/Iout = 1/(Gm2*Gm1*Ro,inv).
The cap on node Vb makes the impedance at that point go down with frequency, making Ro,inv get smaller. But the Ro,inv term is in the denominator of our Zin equation, so it makes the test impedance get bigger as frequency increases. Replace Ro,inv with the impedance of the cap, and you have a rough approximation of the impedance of the gyrator.
Anyone up for a discussion regarding the mosfet sizing ?