Unlike the VFB Op Amp which allows a very wide range of feedback resistor values, RF in a CFB amplifier is specified as a design parameter. Within the allowable range, however, the equipment design engineer can control the response of the amplifier, particularly with regard to the amount of peaking needed in the circuit design. This chart shows the empirical data for one Texas Instruments CFB Op Amp, the LMH6715. The gain is fixed at +2 and the amplitude and phase is plotted here for a range of frequencies. Higher values of RF such as 700 ohms result in the onset of amplitude roll-off at a lower frequency than does a lower value RF such as 300 ohms. For example, a 700 ohm RF produces a one db roll-off at 100 megahertz, whereas a 300 ohm resistor produces a one db roll-off at 300 megahertz, much higher. Notice the phase response for each does not change dramatically. Also, note that the RF range is confined to the range of 200 ohms to about 700 ohms as shown here.