I'm interested in implementing the automatic gain control circuit shown in figure 67 on page 31 (described on page 30). Does somebody know the response time that can be achieved with this circuit? We're trying to calculate this for ourselves but I've been told we need to know the open loop gain of the ADL5519's output amplifiers on OUTN and OUTP. Do you have a spec for the Aol of these amplifiers?
The speed of the op amps really won't be the limiting factor in this type of application. The two dominant factors are: The speed of the log amp and how fast can the VGA which is being controlled switch.( the ADL5519 has a very fast rise time so it won't have much impact) The filtering capacitors which are required, will slow the overall response of the system. This is actually desirable because if the loop speed is set too fast, the VGA will never be able to settle at the desired level. The AD8315 datsheet has a detailed explanation of control loop dynamics.