[SOLVED] Actively loaded differential pair - need help with simulation results

[glenhadlee]

Hi,

Below is the schematic with which I need help.



I want to calculate the following parameters using Spectre but am not sure how to go about doing it-
1.) Input common mode range
2.) Output resistance
3.) Differential gain
4.) Unity gain frequency
5.) Input referred thermal noise at 1 MHz

Transistors M1, M2, M3 and M4 have a W/L of 48u/240nm and transistors M5 and M6 have a W/L of 96um/240nm.

Based on my understanding, M6 and M5 are behaving as a current mirror and M6 is being biased to 100uA in saturation by the 100uA current source. M3 and M4 also form a current mirror and hence 50uA is flowing through each of them(M3 and M4). I need a Vgs-Vth=0.2V for transistors M1 and M2.

I have already extracted the unCox' value, Vth(0.4805V) and lambda for the transistors.

Based on Vgs-Vth=0.2 for M1 and M2, I have estimated the gm to be - gm = (2*Id)/(Vgs-Vth) ~= 0.5E-3 S (since Id has to be 50uA in saturation). I have also estimated the unity gain frequency - ft = (gm)/(2*pi*CL) ~= 39.79MHz

Can someone please provide some suggestions on how to go about calculating these results using Spectre? I want to simulate and obtain the results using Spectre.

 

[Dominik Przyborowski]

To check small signall parameters like transconductance or drain-source resistance, You need only dc analysis of amplifier working with the simplest negative feedback (e.g. as noninverting voltage follower) and print dc operating points of transistors. For GBP You need to run simple ac or stb simulation. Do You using cadence virtuoso or running netlist directly?

BTW. For this currents and fets dimensions I think your transistors works in moderate inversion so your gm probably much differ than 500uS.

 

[glenhadlee]

Hi,

I am using cadence virtuoso directly.

 

[AMSVJ]

1.) Input common mode range
short v0 and vin+ pin, choose dc analysis and sweep vin- from 0 to vdd.. plot vin- and v0
2.) Output resistance
connect vdc from analoglib at v0 pin, choose dc analysis and sweep vdc form 0 to vdd, plot v0 and I(vo) from that calculate R
3.) Differential gain
connect vdc and give ac magnitude as 1 phase 0 for vin+ and phase 180 for vin- , do ac analysis and plot 20log(out+/out-).
4.) Unity gain frequency
5.) Input referred thermal noise at 1 MHz