funberry
Junior Member level 1
Hi everyone
I know that traditionally, an op-amp connected as a comparator consistently underperformed dedicated comparators in most respects.
But that was when we were comparing a 741 and a 311.
Op-amp technology has progressed faster than comparator technology.
We have today op-amps with exceptional speed, which I would expect to perform much better as a comparator.
To the point: I need a fast comparator, response time under 40ns. I don't have a fast comp, but I do have an LMH6655 (with 250MHz BW, 200v/us slew rate, 180mA output current). Can I expect this fast Op-amp to carry over his speed qualities to the comparator role?
One thing I'm questioning ( and please correct me on this) is the output topology. In an Op-amp, the output is a totem-pole, with transistors biased for best linearity, symmetrical current sourcing /sinking, and low current consumption. They're not optimized for being constantly slammed against the rails.
In a comparator, no attention is paid to linearity, noise, bias, etc, just to switching and avoiding saturation.
I'm concerned that ANY op-amp, no matter how fast, is susceptible to saturation if driven to the rails, leading to delays in coming out of saturation.
Are there any fast op-amps that have anti-saturation circuitry built-in? Or some for which saturation recovery delays may still be short enough to meet my 40ns response time need?
Thanks
Andy
I know that traditionally, an op-amp connected as a comparator consistently underperformed dedicated comparators in most respects.
But that was when we were comparing a 741 and a 311.
Op-amp technology has progressed faster than comparator technology.
We have today op-amps with exceptional speed, which I would expect to perform much better as a comparator.
To the point: I need a fast comparator, response time under 40ns. I don't have a fast comp, but I do have an LMH6655 (with 250MHz BW, 200v/us slew rate, 180mA output current). Can I expect this fast Op-amp to carry over his speed qualities to the comparator role?
One thing I'm questioning ( and please correct me on this) is the output topology. In an Op-amp, the output is a totem-pole, with transistors biased for best linearity, symmetrical current sourcing /sinking, and low current consumption. They're not optimized for being constantly slammed against the rails.
In a comparator, no attention is paid to linearity, noise, bias, etc, just to switching and avoiding saturation.
I'm concerned that ANY op-amp, no matter how fast, is susceptible to saturation if driven to the rails, leading to delays in coming out of saturation.
Are there any fast op-amps that have anti-saturation circuitry built-in? Or some for which saturation recovery delays may still be short enough to meet my 40ns response time need?
Thanks
Andy