MCP616-ISLASHMS datasheet(19/38 Pages) MICROCHIP

19 / 38 page

DS21613C-page 19

MCP616/7/8/9

4.9.3

THREE OP AMP

INSTRUMENTATION AMPLIFIER

A classic, three-op amp instrumentation amplifier is

illustrated in Figure 4-11. The two-input op amps

provide differential signal gain and a common mode

gain of +1. The output op amp is a difference amplifier,

which converts its input signal from differential to a

single-ended output; it rejects common mode signals at

its input. The gain of this circuit is simply adjusted with

one resistor (RG). The reference voltage (VREF) is

typically referenced to mid-supply (VDD/2) in single-

supply applications.

FIGURE 4-11:

Three-Op Amp

Instrumentation Amplifier.

4.9.4

PRECISION GAIN WITH GOOD

LOAD ISOLATION

In Figure 4-12, the MCP616 op amp, R1 and R2 provide

a high gain to the input signal (VIN). The MCP616’s low

offset voltage makes this an accurate circuit.

The MCP606 is configured as a unity-gain buffer. It

isolates the MCP616’s output from the load, increasing

the high gain stage’s precision. Since the MCP606 has

a higher output current, and the two amplifiers are

housed in separate packages, there is minimal change

in the MCP616’s offset voltage due to loading effect.

FIGURE 4-12:

Precision Gain with Good

Load Isolation.

OUT

–

() 1

---------

⎝⎠

⎜⎟

⎛⎞ R

------

⎝⎠

⎜⎟

⎛⎞

REF

MCP617

VREF

MCP616

MCP617

VOUT

OUT

IN 1R2 R1

⁄

()

MCP616

VOUT

VIN

MCP606

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