I've been having some trouble with a prototype circuit using the ADA4817-2. My circuit uses that dual amp as the input of a 3-amp IA - with a gain of 2. I am trying for 500MHz BW. The input amp peaks and is prone to oscillate around 180Mhz. I tried everything and couldn't get the circuit stabilized.
Finally - I got an evaluation board (see attached UG083).
I installed a single ADA4817-1 and the following components (refer to fig 2 of eval board guide):
C3, C4 33uF
C5, C6 .47uF 0603 ceramic
C2 .047uF 0603 ceramic
R6, R7 1kohm (jumper to not power down)
R5 274ohm
R3 10ohm
R4 49.9ohm
R9 49.9ohm
R1,R2,R8,R10,C1 not installed
I am running the part at +/-5V supplies, and the thermal pad is tied to gnd.
This should be a simple unity gain follower. I swept the frequency response (50ohm source and load) into a scope. The orange trace (F5) is the max of the FFT. You can see that the output is about -6dBm (with a 0dBm input) at 10MHz - and this peaks up by about 5dB at around 190MHz - then the amplitude 'jumps' and then drops down with increasing frequency. This seems to be a near oscillation. This is nearly identical to the response that I get on my circuit.
(See attached file: eval_amp_freq1.png)
The data sheet warns of peaking at unity gain, but it should be within reason with 274ohm fb resistor. The data sheet specifies a G=1 BW of 1050MHz - and I'm not even getting half that, with instability.
I could sure use some help in getting this device to work. I would think by using the AD eval board I would get very similar performance to that shown on the data sheet.
