At this setting the signal is shared equally between the test resistance and the input impedance of the amplifier, meaning that the resistance and impedance are equal. The resistance at the amplifier input should then be increased until the output waveform is exactly half its previously set value. The display on the oscilloscope screen should be as large as is practical and set so that its amplitude and half its amplitude can be easily estimated. The amplitude of the input signal should be adjusted so that the display on the oscilloscope is noise free (large enough) and distortion free (not too large). The signal generator is set to provide a sine wave output at 1kHz. An oscilloscope or AC voltmeter is connected across the amplifier load (e.g. A variable resistor or a decade resistance box is connected between the signal generator and the amplifier input and its resistance is set to zero Ohms. The set up for measuring input impedance is illustrated in Fig.
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