I am trying to design a circuit to achieve a gain of 10 for input signals up to 50MHz. I have looked at LTC6253 as a possibility, since it has quite a large GBP of 720MHz. If my understanding is correct, for a gain of 10, it should handle up to 720/10 = 72MHz
I have done a simulation on LTSpice, of non-inverting op-amp with a gain of 10 but it shows that the bandwidth would end up being around 35Mhz.... See screenshot below.
The datasheet recommends to use a capacitor in the feedback loop to compensate stray capacitances (C1 in my simulation). Through trial and error I have found this to be around 0.5pF.
It seems there are other parameters I need to consider when selecting my op-amp for this application. Does anyone have any suggestions as to what causes a reduction in effective bandwidth vs what I would have expected from the GBP?
Hi Qbort: The 2GHz spec is the gain-bandwidth-product. It is the product of gain and frequency at a relatively low frequency. In this case, the GBW product was specified at 10MHz, and indicates a typical gain of 200 (46dB) there.
In a gain of 10, consulting the Gain-Phase curve, you should expect a bandwidth of about 85MHz (on a 5V supply, less on a 3V supply). I suspect the problem is that your resistor values are too high, so you are up against the feedback pole and necessary compensation. I suggest you try again with resistor values of 200:450 instead of the 1k:9k, and you should be able to get significantly higher bandwidth.
Thank you for your reply.
I have tried as you suggested of lowering the resistor values (I assume you meant 50:450, for a gain of 10), but saw no noticeable difference. I have even removed the compensation capacitor but it just means the output overshoots (See screenshot below), and maybe marginal increase in bandwidth to 45MHz, but I would expect a bandwidth of at least 72MHz if the GBP is 720MHz and the gain is 10?
Also, just to point out, I think you might be getting confused with a different part? There is no mention of 2GHz in the datasheet of the LTC6253. The GBP is 720MHz as shown on the front page (see extract below).