The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> AC Gain vs Transient Gain
https://designers-guide.org/forum/YaBB.pl?num=1542423186

Message started by MWJ1975 on Nov 16^th, 2018, 6:53pm

Title: AC Gain vs Transient Gain
Post by MWJ1975 on Nov 16^th, 2018, 6:53pm

Hi,

I am using Cadence Virtuoso Spectre Circuit simulator and am measuring significant differences from my transient gain and the gain from my AC analysis.

For my circuit, my amplifier has a matching network for 2GHz for 50ohm impedance. The measured S11 is around -30dB. In the port configurations, I set up my small signal parameters to measure the AC gain. The value measured at 2GHz was about 30dB.

When I'm performing a transient simulation (port still connected), I am using the parameter in the port settings for the input power (dBm). I set this value to -50dBm. From comparing online, the peak value should be 1mVp for 50ohm matching. Which I'm measuring at my input port.

At the output of my amplifier, I should be measuring a -20dBm signal (30mVp). This is not the case. I am measuring about half the value. And the gain calculated from the transient is only 20dB.

I know for a fact there is no clipping involved since the voltage levels are so tiny and I'm using a 1.8 supply. I have also ensured that they are both peak voltage quantities.

Update: I tested at 2.04GHz and the voltage was 40dB (transient). Which seems impossible. The AC gain was only 28dB at this frequency.

Any thoughts? Thanks.