# diode clipper circuit and oscilloscope/function generator problems

#### ninjaman

Joined May 18, 2013
324
hello,

i have a 5 in 1 oscilloscope
http://www.ebay.co.uk/itm/PC-USB-2CH-20M-Digital-Oscilloscope-Spectrum-Analyzer-DDS-Generator-Sweep-B-/111690731978?hash=item1a014951ca:g:nWgAAOSwYGFUs8Eh

i am trying to get this clipper circuit working,
http://www.electronics-tutorials.ws/diode/diode-clipping-circuits.html

i can get the waveform but not with the correct (same) value. i cant get the (approx) 0.7 volts. i have tried using the function generator but i am having problems understanding how the bias and amplitude work. there are no instructions with this and there are only two knobs on the device (bias/amplitude).
i have tried to look at what these do but cant find an easy explanation.
i think that dc bias (if thats what this is?) is there for adding to a voltage that is too small to measure(?).....is this correct?
amplitude is simply there to provide a sine wave of so many volts.....?

any help or advice with this would be great.
how could i measure the dc bias on the scope?

also, the clipper circuit i am using, i have a 1kohm resistor and 1n4004 diode.
thanks

simon

#### dl324

Joined Mar 30, 2015
11,314
how could i measure the dc bias on the scope?
Set the input to DC coupling.
the clipper circuit i am using, i have a 1kohm resistor and 1n4004 diode.
What is the peak to peak input voltage? What voltage are you measuring and what are you expecting?

#### ninjaman

Joined May 18, 2013
324
i am expecting to see 0.7volts positive and the rest negative.
with the dc bias thing, i am having a problem with understanding how it works and adjust it so it wont affect the results (the 0.7 volts mentioned above).

#### dl324

Joined Mar 30, 2015
11,314
i am expecting to see 0.7volts positive and the rest negative.
What is the peak to peak input voltage? What voltage are you measuring and what are you expecting?
Does the input have any DC bias?

#### ninjaman

Joined May 18, 2013
324
i dont have a clue, i have been trying to figure out this bias thing on my scope. on the scope function there is a tab called "more" in here you select either ac or dc, invert, verticle offset, calibration which has bias in mV and amplitude 0.1 to 10. then on the physical body of the scope there is a bias knob and an amplitude knob. neither of these have settings just the words bias and amplitude next to them. when i try to make a measurement the readings that i am getting are all over the place.
i can view voltage:
• max,
• min,
• rms,
• pk-pk.
the min is always a few more than the max, for example the max volt may say 705mV and the min would say 495mV.
i just set the calibration on the scope to:
• vertical offset -341mV,
• bias 1mV,
• amplitude 0.1.
i then get a voltage max of 206mV and a min of -3.58mV with an rms of 125mV and a pk pk of 210mV?????????????

is there a good tutorial on this stuff anywhere.
this is something i need to master before moving on.

thanks for your input so far dl324

#### dl324

Joined Mar 30, 2015
11,314
Set coupling on the "more tab" to AC; this will AC couple the signal so any DC bias will be removed. Set vertical offset to zero if this puts the trace in the middle of the screen.

What is the peak to peak amplitude of the input signal?

Can you post a screen shot of the waveform you're seeing? Do you have two channels so you can also display the input signal?

#### ninjaman

Joined May 18, 2013
324
hello,

this is the screen shot, with the settings you recommended. the minimum value is always a little more than the max. i have measured 0.3 volts on the multimeter ac setting

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#### dl324

Joined Mar 30, 2015
11,314
It appears that channel 2 is turned off; I assume that's the clamper output.

The amplitude of the input is too small to forward bias the diode. The diode won't clamp unless it's conducting. Increase amplitude to a few volts peak to peak.

#### ninjaman

Joined May 18, 2013
324
hello

i am having a hard time with this dds on my scope. i have tried to set it to sine wave at 50Hz. there is an amplitude and bias controls on the scope body. and in the software there is a calibration menu with bias and amplitude. i have attached the scope probe to the output of the dds and tried to measure it. what is the bias supposed to be and what is the amplitude supposed to be. when i turn the bias control one way the sine waves top gets less until have waveform, when i turn the bias the other way the bottom becomes less until half wave form. the amplitude is set to 1. i think that means that it is 1 * 5 volts. when i change it to 2 i get 10 volts showing.

i currently have the amplitude knob full anti clockwise with 8.72 volts peak to peak on the scope, 4 volts max and -4.720 volts min. the software calibration is saying amplitude of 1 and bias of 1mv. when i change the bias to 37 mv the min and max become the same.
any help would be great.
also, i have done some research on using bias on a function generator but cant seem to find the answer to this problem.

#### dl324

Joined Mar 30, 2015
11,314
i currently have the amplitude knob full anti clockwise with 8.72 volts peak to peak on the scope, 4 volts max and -4.720 volts min. the software calibration is saying amplitude of 1 and bias of 1mv.
You should be able to see the clamp circuit working with a 4V peak signal.
when i change the bias to 37 mv the min and max become the same.