by Rana Naeem » Sat Feb 13, 2010 5:39 pm
Most absolute-value circuits have limited bandwidth and high component count, and they require several matched resistors. The circuit uses three fewer components than most absolute-value circuits require, and only two of the resistors must have 1% tolerance to obtain 1% accuracy. This circuit's output voltage is an accurate representation of the absolute value of the input signal, and it is accurate for input signals containing frequencies as high as 10 MHz. Another advantage of this circuit is that it has a positive-voltage output, thus saving an analog inverter in most applications. When the input voltage is positive, the negative output voltage of IC1 cuts off the diode, thereby preventing signal propagation through IC1. Virtually no signal propagates through R2, because the resistor connects to ac ground through the output of IC2. The only signal path is through R3 to buffer IC2, and the output of the buffer is a positive voltage.