Hi all,
The goal is simple: I want to build a non-inverting opamp circuit with a 10K linear potmeter (the MAX5389 digital potmeter, to be precise), with a gain between 1/10 and 10, depending on the potmeter's wiper position. Ideally, I get 1/10 with the potmeter in the lowest position, 1 (unity gain) in the middle position, and 10 in the highest position.
Problem: I have no negative supply rail, the input signal is always positive, and the ground reference is also the opamp's lower supply voltage, so any inverting stage is out of the question -- which is a bit of a shame, of course, since that would offer an almost trivially simple solution.
Of course I can simply build a (roughly) 10x amplifier with a 100K/10K resistor divider as a negative feedback loop, and feed the + input through the potmeter in standard volume control configuration (signal fed in the top, bottom to ground). This, however, has a severe drawback: for unity gain, the potmeter must already be turned nine-tenths down, and lower gains are even trickier to set. Also, the opamp itself is always set to the maximum gain of 10, which isn't optimal from a noise point of view.
I've been toying around with several configurations, but especially the less-than-unity gain range is presented me with a bit of a challenge. Can anyone offer a smart solution to this little puzzle?
Thanks in advance,
Best regards,
Richard Rasker