Other Parts Discussed in Thread: LMH6517, THS4541, THS3217, THS3215, OPA691, OPA2677, OPA2695
Hello,
I need to drive a 50 ohm load up to 8.9Vpp (23dBm) 5 MHz to 30 MHz from the output of a LMH6517 programmable gain amplifier. The LMH6517 can produce max 5.9Vpp differential. I have power rails of 5V and 3.3V. I used an OPA2832 in a bridge for gain. My approach is distorted when I crank up the Vpp output. Can someone suggest a chip that I can put after the LMH6517 or a correction to my approach?
On both differential outputs of the LMH6517, I put OPA2832 op amp as non-inverting amplifier of gain of 2 with GND and 5V on the supply rails. The OPA28322 is spec 75MHz BW for gain of 2. The datasheet says it can do 4.9Vpp for 5V supply and further it talks about an output range of 0.3V to 4.6V with 150 ohm load. It is not talking about a 50 ohm load anywhere so my part selection is possibly wrong because I need to drive 50 ohm.
I tied both op amp outputs to a mini circuits ADTT1-1+ transformer. The sine wave is not round at high frequency and high amplitude. For example, at 10MHz 3Vpp output, it is no longer fine at the output pin 1 of the op amp. Below 3Vpp, it is a nice sine. I took a photo of an analog scope. The bottom curve is the op amp output at 1V/div. The top curve is the mini-circuit transformer output after an 50 ohm attenuator. What part can I use to drive closer to the rails?
Thanks,
Frank