I'm happy to answer your questions! They're quite valid.
I haven't yet prototyped this yet, but if you plan to use it at high frequencies (<10MHz), dead bug is the way to go. There is parasitic capacitance between the metal strips of the breadboard that would mess up your prototype.
I did look into a few options before choosing a multiplier. It basically comes down to bandwidth again:
- Digital potentiometers don't have high enough bandwidth (signals at high frequencies get attenuated). I assume this is what you meant by a voltage divider as the point of the amplitude control is to allow variable amplitude.
- Varying the gain on an op-amp drastically changed its frequency response, and gains above 2 or so will cut back the frequency response a lot.
- Programmable gain amplifiers (often used in RF circuits) are few and far between and most of them weren't suitable.
The op-amps were mainly chosen for speed and slew rate. I was originally going to use the THS6022, but it's slew rate would not have let me output a 40MHz signal at +/- 10V. The slew rates had to be over 2800V/us (c475p calculated that) so I went for well over that to be on the safe side. The fairly high frequency also cut down my options more that I had thought it would; when you have a gain of 5 there are very few, if any, op-amps with a high enough slew rate. This is why I went for a dual configuration with 2 op-amps daisy-chained; they would each have a lower gain which gave me more options. I chose the THS3001 (the first one) partly because I already had one
and mostly because it has an excellent frequency response which is well documented. I chose the ThS3095 because it also has a good frequency response and can easily supply the required 200mA (10V, 50 ohm load). The resistors for them were chosen by looking I. The datasheets, which recommended specific values for certain gains to get the optimum frequency response.
I wouldn't describe myself as an analog person either!
~Richard
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