Phase compensating capacitor! Well.. In a two stage OTA topology, for miller compensation, we introduce a capacitor between two stages.. That capacitor moves the dominant pole to lesser frequency and second dominant pole to higher frequency! By this we get a higher unity gain frequency!
That means a capacitor is connected in the feedback loop to compensate the op-amp frequency response. The miller compensation circuit is shown below. In this technique, a capacitor is connected to the feedback with a resistor across the output.
Objective of compensation is to achieve stable operation when negative feedback is applied around the op amp. Miller - Use of a capacitor feeding back around a high-gain, inverting stage. Miller capacitor only Miller capacitor with an unity-gain buffer to block the forward path through the compensation capacitor. Can eliminate the RHP zero.
Note that compensation capacitor Cc can be treated open at low frequency. It should be noted again that the hand calculation using the approximate equations above is of only moderate accuracy, especially the output resistance calculation on rds. Therefore, later they should be verified by simulation by SPICE/SPECTRE.
In this system, the phase compensation is configured by connecting resistor RITH and capacitor CITH in series with the output of the error amplifier . Rea represents the output resistance of the error amplifier, Vref is the reference voltage, and VFB is the feedback reference voltage (Figure 1). Figure 1. Phase compensation circuit diagram 2.
The internally Compensating Network in Op Amp use a metal oxide capacitor built within the IC. The circuit configuration is given in Fig. 35.3. Although this works well, internal compensation does not allow us any control over the op-amp frequency response. The 301 and 709 op-amps have no internal frequency compensation capacitor.