5-4. Amplifier Overload Characteristics
The overload point for some amplifiers is difficult to determine by using sinewave
input. The triangle waveform is ideal for this type of test because any departure
from absolute linearity is readily detectable. By using the triangle output, the peak
overload condition for an amplifier can be readily determined. This overload
FIG 6. condition is shown in shown in
5-5. Amplifier Performance Evaluation Using Square Waves
The standard sinewave frequency reopens curves do not give a full evaluation of
the amplifier transient response. the square wave, because of the high harmonic
content, yields much information regarding amplifier performance when used in
conjunction with an oscilloscope.
A. Use the test set-up of FIG 7. The 50
Ω
termination at the amplifier input is
essential when using square waves to eliminate the ringing effects generated by the
fast rise times.
B. Using the triangle output, set the AMPLITUDE control so that there is no
signal clipping over the range of frequencies to be used.
C. Select the square wave output and adjust the frequency to several
check points within the pass band of the amplifier such as 20 Hz, 1000 Hz and 10
KHz.
D. At each frequency checkpoint, the waveform obtained at the amplifier
output provides information regarding amplifier performance with respect to the
frequency of square wave input. FIG 7. indicates the possible waveforms obtained
at the amplifier output. Square wave evaluation is not practical for narrow-band
amplifiers. The restricted bandwidth of the amplifier cannot reproduce all frequency
components of the square wave in the proper phase and amplitude relationships.
Input Waveform
Output Waveform
