Using a DAC to control a FET resistance seems like it would be a lot simpler, although this might not be in the spirit of the exercise. I would also be inclined to control the feedback resistance rather than the input resistance.
Yeah, "spirit of the exercise" is part of it as this video jumps off of the inverting summing amplifier video. I would only use this if the requirements were minimal. There are certainly other means to achieve digital gain control, and with higher resolution, range, and accuracy. But this is, as the title states, a simple means to achieve that end.
Great videos. How do you create a audio log pot? I have made one with the 40xx series and alot of resistors. Uses a dual clock for stepping. In the days when all digital pots where very noisy (early 80') it worked good but could not replace a mechanical pot due to size.
The gain ratios would be logarithmic. A bit of a pain to calculate compare to this, and I'll add that this technique isn't really intended for a wide gain range with fine control.
If I was doing this from scratch, I'd use analog switches instead of the JFETs (as indicated in the side notes). The point of using the JFETs is for illustrative/learning purposes.
I think for switching, also it's possible to use two mosfets back to back, that way their body diode create a true block of current when you switch them off.
Using a DAC to control a FET resistance seems like it would be a lot simpler, although this might not be in the spirit of the exercise. I would also be inclined to control the feedback resistance rather than the input resistance.
Yeah, "spirit of the exercise" is part of it as this video jumps off of the inverting summing amplifier video. I would only use this if the requirements were minimal. There are certainly other means to achieve digital gain control, and with higher resolution, range, and accuracy. But this is, as the title states, a simple means to achieve that end.
Great videos. How do you create a audio log pot? I have made one with the 40xx series and alot of resistors. Uses a dual clock for stepping. In the days when all digital pots where very noisy (early 80') it worked good but could not replace a mechanical pot due to size.
The gain ratios would be logarithmic. A bit of a pain to calculate compare to this, and I'll add that this technique isn't really intended for a wide gain range with fine control.
JFETs are kinda rare in Hungary, I can find only 2-3 types of that.
I guess it’s not so frequently used in everyday electronics.
If I was doing this from scratch, I'd use analog switches instead of the JFETs (as indicated in the side notes). The point of using the JFETs is for illustrative/learning purposes.
I think for switching, also it's possible to use two mosfets back to back, that way their body diode create a true block of current when you switch them off.