My application needs to operate in the ISM-915 MHz on the RF side. At the same time,my application requires analog baseband with 1 V p2p IQ (for each IN, IP, QN, QP).
I'm using ADRF6850 as RX front-end since it provides analog IQ. The internal gain from 0 to 60 dB is set by external voltage (VGAIN) from 0 to 1.5V. ADRF6850 provides baseband outputs up to 2.5 V p2p.
I need a circuit that adjusts the gain such that baseband output stays around 1 V p2p, regardless of RF input power (unless it is too low). I see two possible options:
1) Get automatic AGC on the RF side and manually set VGAIN such that baseband never exceeds 1 V p2p. This option is less desirable since combined RF from all frequencies will be used to set the gain.
2) Set up closed loop feedback from baseband to VGAIN. This option is proffered since gain is set based on the in-band down-converted power.
Ideally, I want to use a part that can be configured to my specifications, instead of designing my own feedback loop (I don't know what is the feed-forward function of ADRF6850 is to properly design the closed loop).
As a note, 1 V p2p signal will be interfacing with the low-voltage integrated circuit. Attenuator. from 2.5 V to 1 V is not desired because it will lower SNR of the signal, which is critical. Similarly, clipping the BB at 1 V is not possible since it will alter the signal.