# Maximum Symmetrical Swing

#### laguna92651

Joined Mar 29, 2008
101
I need to set up a test to measure the maximum symmetrical swing for a a common-emitter amplifier. Can anyone get me started on the approach?

#### KL7AJ

Joined Nov 4, 2008
2,229
I need to set up a test to measure the maximum symmetrical swing for a a common-emitter amplifier. Can anyone get me started on the approach?
Is this amplifier in existence, or are you trying to design it? I generally like the pragmatic approach. If you have a semi-working amplifier, devise a means of changing the bias voltage. Feed the thing a sine wave, while looking at the output with an oscilloscope. Increase the gain untill you see clipping. If the postive peaks clip first, increase the bias voltage. If the negative peaks clip first, decrease the bias voltage. If the tops and bottoms clip about the same time, you're good to go.

Eric

(See...not a drip nor a drop of nasty old math is necessary!)

#### laguna92651

Joined Mar 29, 2008
101
I've design it and ran it in pspice, and it checks out okay. I am going to build, but after I do I want to measure the max symmetrical swing. So if I vary Vcc and it clips, what would I measure to calculate the max swing. Could I optionally vary the input signal and look for clipping.

#### KL7AJ

Joined Nov 4, 2008
2,229
I've design it and ran it in pspice, and it checks out okay. I am going to build, but after I do I want to measure the max symmetrical swing. So if I vary Vcc and it clips, what would I measure to calculate the max swing. Could I optionally vary the input signal and look for clipping.
Yes...just increase the input still it starts looking squashed.

#### laguna92651

Joined Mar 29, 2008
101
Is the max swing just the peak to peak output before the signal starts to clip either positive or negative? Thanks for the help.

#### KL7AJ

Joined Nov 4, 2008
2,229
Is the max swing just the peak to peak output before the signal starts to clip either positive or negative? Thanks for the help.
Generally, you'll see a little "harder" clip on the positive peak. So, depending on how much non-linearity you can tolerate, this point may be a bit harder to define. (It's very well defined in a push-pull/complementary configuration!) But yes...by definition, it's peak-to peak. A good class A voltage amp should have a p-p swing of good linearity about equal to 80% of your supply voltage.

Eric

(Depending on the text, "swing" could be defined as half that value. I'd avoid the use of the word swing in favor of p-p capacity, or something like that, to avoid ambiguity.)

eric