RadioBanter - View Single Post - Ringing on square wave: how to eliminate?

October 19th 03, 12:34 PM

On 19 Oct 2003 03:44:51 GMT, (Fred McKenzie) wrote:

Paul-

The next stage has some kind of input impedance, whether it is a logic gate or
an analog amplifier. I'm saying that you may be able to adjust that impedance
for minimum ringing.

If it is a logic gate, can you add a pull-up resistor across the input? If it
is an amplifier, can you add a resistor across the input without upsetting the
bias? Trying several values, you may be able to make an improvement.

Why is a long ground lead a bad thing? Because wire has inductance. Above
some frequency it can no longer be considered a short circuit. The longer the
wire, the lower the frequency. Your ringing contains frequencies that are
multiples of 8 MHz.

In addition to keeping scope probe wires short, have you compensated the probe?
Many scopes have a square wave calibration source available for checking
calibration. Another thing you can use it for, is to adjust the probe for
minimum overshoot and rounding of the waveform. (The adjustment allows you to
make the scope's probe-to-input capacitance ratio the same as its resistance
ratio.)

Thanks, Fred. I'll make a mental note of that lot.
--

"Windows [n.], A thirty-two bit extension and GUI shell to a sixteen bit patch
to an eight bit operating system originally coded for a four bit
microprocessor and produced by a two bit company."