I reoptimized the gain of the TTFSS, and measured the OLG of the TTFSS loop. The UGF is 150 kHz.

  To optimize the gain, I observed the noise from MIXER OUT while adjusting the gains. As the gain increases, the noise at MIXER OUT will be suppressed. I didn't see any oscillation even though the gain was set to maximum, but oscillation occurs once I injected the excitation, so I reduced fast gain. Phase margin might not be enough. I also used 10dBm attenuator on the LO input instead of 12dBm to get 10dBm input.

The gain setting are

FAST: 980

COMMON 1000

I measured the TF, as described here. The result is plotted below. The UGF is @150 kHz. It is lower than we thought.