Here is the customer issue;
The question is regarding the OPA209.
We have an OPAMP DC amplifier for a loop filter with Av = 5.7 It is configured as a single bias at 20V.
At the middle frequency, Vin = 0.92 V, Vout = 5.2 V.
At the highest frequency, Vin = 2.48 V, Vout = 14 V.
We replaced the OPAMP that is a 15 nV/rtHz with the OPA209 to improve the Phase Noise.
At the middle frequency, the Phase noise degraded by at least 10 dB when we used the OPA209.
At the highest frequency, the Phase noise improved by 5 to 10 dB.
The Hittite engineer said that maybe the input voltage is too low for the middle frequency, and it is close to ground. But he also noted that the OPA209 is a rail-to-rail.
His suggestion is to make the OPAMP configuration to a dual supply.
The question is if the OPA209 really is rail-to-rail, should we be having that problem ?
Also, what is the PSRR of the OPA209.
Comments....
-Tom-
