How can we design a simple circuit to tune the slew rate o an ideal square waveform

[bhl777]

Hi All, I have a general question about the slew rate control of the periodic square waveform. If we have the ideal square waveform whose slew rate is inifite, how can we use some logi circuits and RC components to tune the slew rate of this signal? Thank you!

 

[crutschow]

What's the frequency range of the waveform?

If you want a linear rise and fall time, then you need to use some type of integrator on the square-wave.

 

[bhl777]

What's the frequency range of the waveform?

If you want a linear rise and fall time, then you need to use some type of integrator on the square-wave.

Hi crutschow, the range is around 1kHz to 50kHz. Would you teach me how to use the integrator? Thank you!

 

[BradtheRad]

Put in a series capacitor which gives a spikey waveform.
Add resistors in different positions relative to the capacitor (in series with it, in parallel with it, other end to ground or supply+, etc.).
Play with values until you see your leading edge become more square. Expect amplitude to drop a little.

 

[crutschow]

Is the pulse a fixed amplitude or varying?
Can the output be a fixed amplitude?

 

[BradtheRad]

Now I realize I misunderstood when I posted how to restore the edge so it rises more quickly. You want to create a ramp appearance. Then the capacitor should be installed between the signal and ground, to create the integrator as recommended in post #2.

 

[E-design]

One way is to use a programmable current source to vary the slew rates as shown below. A lot will depend on required frequency, level, etc.

 

[crutschow]

Here's the LTspice simulation of a slew rate control circuit using two complementary current mirrors to generate a constant charge and discharge current into a capacitor (C1).
This generates a linear ramp for the rise and fall of the pulse.
Pots U1 and U2 control the rise and fall times respectively.

 

[crutschow]

Here's the simulation showing a variation in rise/fall times with pot adjustment.