Quote: Your 5pF capacitors are connected to virtual grounds, so they will not be much help in suppressing the LO if the TIA still has much gain at the LO frequency.
Actually I think if the TIA inputs are virtual grounds at the LO frequency, then the TIA will filter the LO at the output. If they are not, then the 5pF capacitors will help.
Quote:But now a day people are directly connecting the Mixer to the RF input instead of using LNA. I wonder how that fares for signal like GSM of -99dBm....
I'm not sure if it is done in commercial products. Maybe ones where performance requirements are very relaxed. Leaving aside the noise performance, there is not much isolation from the LO to the antenna, so the unwanted LO emmission would be very high.
regards,
Aaron