"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

Lead-Lag Compensation
7-18
FHASE (Aβ
dB
0dB°
–45°
–135°
–180°
1/τ1
Figure 7–19. Compensated Attenuator Bode Plot
20 Log (Aβ )
)
Without CF
1/τ2
Without CF
1
RFIIRGCG
With CF
With CF
Log(f)
The inverting and noninverting closed-loop gain equations are a function of frequency.
Equation 7–21 is the closed-loop gain equation for the inverting op amp. When R FC F =
R GC G, Equation 7–21 reduces to Equation 7–22, which is independent of the breakpoint.
This also happens to the noninverting op amp circuit. This is one of the few occasions
when the compensation does not affect the closed-loop gain frequency response.
When R FC F = R GC G
VOUT
VIN 7.8 Lead-Lag Compensation
R F
R F C F s1
R G
R G C G s1
VOUT VIN R F
R G
(7–21)
(7–22)
Lead-lag compensation stabilizes the circuit without sacrificing the closed-loop gain performance.
It is often used with uncompensated op amps. This type of compensation provides
excellent high-frequency performance. The circuit schematic is shown in Figure
7–20, and the loop gain is given by Equation 7–23.