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Tracey3 said:capacitor C3 acts as a low pass filter
Tracey3 said:I don't quite understand the purpose of C1 and C2 as indicated on the picture.
Excellent point Jim! I totally missed that.jim hardy said:it allows no return path for "input bias current". so probably won't work.
It isn't ...if you had read the following posts you would have seen that Tracy3's error was correctedalan123hk said:Why C3 acts as a low pass filter ?
My logic goes like this.jim hardy said:Maybe a PLL building block ?
This simulation runs for 100msec but I only show the last 2 msec. The DC levels are still settling down to a steady state. Changes in duty cycle are much greater due to variation of the DC level than they are due to input frequency.jim hardy said:So the output's DC content changed , but as a result of frequency or waveshaps?
A low-pass filter on the output, with a DC meter, would show mainly duty cycle variations while C3 charged and settled down. I could write a more complex script that set the capacitor initial charge voltage, but first we would need to better define the DC bias.jim hardy said:What would a DC meter on output show ?
berkeman said:Excellent point Jim! I totally missed that.
Interesting thought, I'd never considered that before. I'll have to check some typical datasheets. Do you think that will still be true at -40C? Do you know approximately what the reverse leakage current is over temperature for typical protection diodes inside opamps? And the top and bottom clamp diodes are probably not typically matched very well, I would think. I'll have to think about how they could combine to provide a center-bias voltage. (Maybe there is a patent in there for you somewhere...)analogdesign said:If it is a CMOS comparator the input bias current will be low enough that it can probably be supplied by the ESD diodes on the input pads. I don't think the input bias current will be a problem here.
analogdesign said:I don't think the input bias current will be a problem here.
Bias is never a problem with a partial schematic. Bias requirements must be resolved by the engineer who implements the circuit. That engineer will take into account the technology employed for that particular implementation.analogdesign said:If it is a CMOS comparator the input bias current will be low enough that it can probably be supplied by the ESD diodes on the input pads. I don't think the input bias current will be a problem here.
Let's not give the impression that op-amps can be used as voltage comparators. Op-amps are designed to operate with very low input differential voltages, so many have input voltage clamping diodes to prevent saturation, while voltage comparators are usually specified to operate with differential input voltages equal to the supply voltage.jim hardy said:I'm old enough to still think in terms of LM193 type comparators, or an op-amp based one.
The problem is not bias current, it is about the common mode voltage range. If the "ground reference" is lost, the common mode voltage has a tendency to drift due to spurious leakage currents. Thus the comparator will suddenly stop working (believe me, I know. I once got an "alarm" call and had to travel by plane to another town only to discover that an electrician had disconnected the analog ground reference for some reason and forgotten to reconnect it).analogdesign said:If it is a CMOS comparator the input bias current will be low enough that it can probably be supplied by the ESD diodes on the input pads. I don't think the input bias current will be a problem here.
The capacitor on the ground connection of a comparator input serves as a noise filter, reducing any unwanted fluctuations or disturbances in the input signal. It also helps to stabilize the voltage at the input, ensuring accurate and reliable comparisons.
The capacitor in a comparator circuit acts as a low-pass filter, allowing only low-frequency signals to pass through. This helps to remove any high-frequency noise or interference from the input signal, resulting in a cleaner and more stable signal for the comparator to process.
The recommended capacitance value for the ground connection of a comparator input can vary depending on the specific circuit and application. Generally, a value between 0.1μF to 1μF is recommended, but it is best to consult the datasheet or design guidelines for the specific comparator being used.
Yes, a capacitor can be added to the ground connection of a comparator input in an existing circuit. However, it is important to consider the effects it may have on the overall circuit and to choose an appropriate capacitance value to avoid any unwanted changes in performance.
One potential drawback of using a capacitor on the ground connection of a comparator input is that it can introduce a small delay in the signal, due to the time it takes for the capacitor to charge and discharge. This delay may not be significant in most applications, but it is important to consider in high-speed circuits where timing is critical.