propagation delay for the ANALOG circuit

[an_82]

Hi,

I have designed an analog circuit, then I applied a square pulse to the input and get the response at the output. For the sake of speed examination, I measured the propagation delay for the output (low to high & high to low delay).

Is it right to measure the propagation delay for the analog circuit like this ?

 

[chuckey]

Keep the signal at a low amplitude otherwise you will be measuring the slew rate. I would expect to see the input square wave have a rise time of , say ten nanoseconds (from 10-> 90%) and the output having a rise time of, say one microsecond, so what is the propagation delay?. It might be 50 nS at the 10% point and 1.1 microsecs at the 90% point.
With a video (wideband analogue ) signal, a carrier sweeps across the band with a low frequency amplitude modulation. The output of the video device then is connected to the input of the test set, where the phase of the low frequency modulation is compared to the original signal. So the output on an oscilloscope is a graph plotting delay time against carrier frequency. This test is done so that all frequency components of a complex wave form take the same time to get through a system, its called group delay.
Frank

 

[an_82]

Keep the signal at a low amplitude otherwise you will be measuring the slew rate. I would expect to see the input square wave have a rise time of , say ten nanoseconds (from 10-> 90%) and the output having a rise time of, say one microsecond, so what is the propagation delay?. It might be 50 nS at the 10% point and 1.1 microsecs at the 90% point.
With a video (wideband analogue ) signal, a carrier sweeps across the band with a low frequency amplitude modulation. The output of the video device then is connected to the input of the test set, where the phase of the low frequency modulation is compared to the original signal. So the output on an oscilloscope is a graph plotting delay time against carrier frequency. This test is done so that all frequency components of a complex wave form take the same time to get through a system, its called group delay.
Frank

Dear chuckey,

Thanks for your reply.

I think you explained rise and fall time (10% & 90%). I mean propagation delay which is computed as t_htl and t_lth. I studied that this delay is typically defined for digital circuits, my question is that by above method, may I compute this delay for analog circuit ?

By the way, slew rate is different with that I said. Slew rate is defined as the rate of changing at the response signal.

 

[chuckey]

The "propagation delay" is equivalent to group delay in analogue circuits. I do not know what " t_htl and t_lth" is or how you computed them.
Frank

 

[LvW]

Hi,

I have designed an analog circuit, then I applied a square pulse to the input and get the response at the output. For the sake of speed examination, I measured the propagation delay for the output (low to high & high to low delay).

Is it right to measure the propagation delay for the analog circuit like this ?

I think, at first it is necessary to know how the ouput signal looks like. Is there a remarkable distortion caused by the limited bandwidth of the system? Are you speaking of a pure analog system?
In general, I doubt if the term "propagation delay" (known from digital circuits) is appropriate because there are some delay sources (phase shift).
Example: If we compare the step response of a simple RC lowpass with the input step - can we define something like a "propagation delay"?

 

[an_82]

I think, at first it is necessary to know how the ouput signal looks like. Is there a remarkable distortion caused by the limited bandwidth of the system? Are you speaking of a pure analog system?
In general, I doubt if the term "propagation delay" (known from digital circuits) is appropriate because there are some delay sources (phase shift).
Example: If we compare the step response of a simple RC lowpass with the input step - can we define something like a "propagation delay"?

Yes the system is pure analog and there are no any delay sources such as phase shifter. It consists of several current mirrors and feedback circuit.