Datasheet
MCP6281/1R/2/3/4/5
DS21811E-page 16 © 2008 Microchip Technology Inc.
FIGURE 4-11: Cascaded Gain Circuit
Configuration.
4.9.3.3 Difference Amplifier
Figure 4-12 shows op amp A configured as a difference
amplifier with Chip Select. In this configuration, it is
recommended to use well-matched resistors (e.g.,
0.1%) to increase the Common Mode Rejection Ratio
(CMRR). Op amp B can be used to provide additional
gain and isolate the load from the difference amplifier.
FIGURE 4-12: Difference Amplifier Circuit.
4.9.3.4 Buffered Non-inverting Integrator
Figure 4-13 shows a lossy non-inverting integrator that
is buffered and has a Chip Select input. Op amp A is
configured as a non-inverting integrator. In this config-
uration, matching the impedance at each input is
recommended. R
F
is used to provide a feedback loop
at frequencies << 1/(2πR
1
C
1
) and makes this a lossy
integrator (it has a finite gain at DC). Op amp B is used
to isolate the load from the integrator.
FIGURE 4-13: Buffered Non-inverting
Integrator with Chip Select.
4.9.3.5 Inverting Integrator with Active
Compensation and Chip Select
Figure 4-14 uses an active compensator (op amp B) to
compensate for the non-ideal op amp characteristics
introduced at higher frequencies. This circuit uses
op amp B as a unity-gain buffer to isolate the integration
capacitor C
1
from op amp A and drives the capacitor
with low-impedance source. Since both op amps are
matched very well, they provide a higher quality
integrator.
FIGURE 4-14: Integrator Circuit with Active
Compensation.
4.9.3.6 Second-Order MFB Low-Pass Filter
with an Extra Pole-Zero Pair
Figure 4-15 is a second-order multiple feedback low-
pass filter with Chip Select. Use the FilterLab
®
software
from Microchip to determine the R and C values for the
op amp A’s second-order filter. Op amp B can be used
to add a pole-zero pair using C
3
, R
6
, and R
7
.
A
B
CS
R
4
R
3
R
2
R
1
V
IN
V
OUT
MCP6285
A
B
CS
R
2
R
1
V
IN2
V
IN1
R
2
R
1
V
OUT
R
4
R
3
MCP6285
A
B
CS
R
F
C
1
R
2
C
2
R
1
V
IN
V
OUT
MCP6285
R
1
C
1
R
2
R
F
||
()C
2
=
A
CS
B
V
IN
V
OUT
R
1
C
1
MCP6285