MCP6291 datasheet(16/36 Pages) MICROCHIP

16 / 36 page

MCP6291/1R/2/3/4/5

DS21812E-page 16

4.9.3.2

Cascaded Gain

Figure 4-11 shows a cascaded gain circuit configura-

tion with Chip Select. Op amps A and B are configured

in a non-inverting amplifier configuration. In this config-

uration, it is important to note that the input offset volt-

age of op amp A is amplified by the gain of op amp A

and B, as shown below:

Therefore, it is recommended to set most of the gain

with op amp A and use op amp B with relatively small

gain (e.g., a unity-gain buffer).

FIGURE 4-11:

Cascaded Gain Circuit

Configuration.

4.9.3.3

Difference Amplifier

Figure 4-12 shows op amp A as a difference amplifier

with

Chip

Select.

this

configuration,

recommended to use well-matched resistors (e.g.,

0.1%) to increase the Common Mode Rejection Ratio

(CMRR). Op amp B can be used for additional gain or

as a unity-gain buffer to 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/(2

πR

1C1) 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 C1 from op amp A and drives the

capacitor with low-impedance source. Since both op

amps are matched very well, they provide a high quality

integrator.

FIGURE 4-14:

Integrator Circuit with Active

Compensation.

OUT

INGAGB

OSAGAGB

OSBGB

Where:

GA = op amp A gain

GB = op amp B gain

VOSA = op amp A input offset voltage

VOSB = op amp B input offset voltage

VIN

VOUT

MCP6295

VIN2

VIN1

VOUT

MCP6295

VIN

VOUT

MCP6295

1C1

()C

VIN

VOUT

MCP6295

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