The Equalizer circuit is illustrated in Fig. 18. This circuit consists
of two matched inverting amplifiers for each of the inputs
INN and INP. The resistor placed between the source terminals
of the two NFETs help program the gain of the circuit.
At lower frequencies, the capacitor acts as an open circuit,
and hence helps set the DC gain of the circuit. The lower
the value of , the higher is the DC gain. Capacitor is, in
effect, a programmable zero that allows the gain to rise as frequency
rises because the impedance of the capacitor reduces as
the frequency rises. Thus, this network can be tuned to provide a
complementary frequency response characteristic to that of the
wiring channel. As a result, the net system frequency response
is flattened and the range of the system frequency response is extended. At high enough frequencies, the amplifiers roll off
and the system becomes unstable. Therefore, NFETs provide
the best choice for this type of equalization circuit. The sole purpose
of resistors and is to generate a common mode
signal.