MCP616 datasheet(15/30 Pages) MICROCHIP

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DS21613B-page 15

MCP616/7/8/9

4.9

Application Circuits

4.9.1

HIGH GAIN PRE-AMPLIFIER

The MCP616/7/8/9 op amps are well suited to

amplifying small signals produced by low-impedance

sources/sensors. The low offset voltage, low offset

current and low noise fit well in this role. Figure 4-8

shows a typical pre-amplifier connected to a low-

impedance source (VS and RS).

FIGURE 4-8:

High Gain Pre-amplifier.

For the best noise and offset performance, the source

resistance RS needs to be less than 15 kΩ. The DC

resistances at the inputs are equal to minimize the

offset voltage caused by the input bias currents

(Section 4.2 “DC Offsets”). In this circuit, the DC gain

is 10 V/V, which will give a typical bandwidth of 19 kHz.

4.9.2

TWO OP AMP INSTRUMENTATION

AMPLIFIER

The two-op amp instrumentation amplifier shown in

Figure 4-9 serves the function of taking the difference

of two input voltages, level-shifting it and gaining it to

the output. This configuration is best suited for higher

gains (i.e., gain > 3 V/V). The reference voltage (VREF)

is typically at mid-supply (VDD/2) in a single-supply

environment.

FIGURE 4-9:

Two-Op Amp

Instrumentation Amplifier.

The key specifications that make the MCP616/7/8/9

family appropriate for this application circuit are low

input bias current, low offset voltage and high common-

mode rejection.

4.9.3

THREE OP AMP

INSTRUMENTATION AMPLIFIER

A classic, three-op amp instrumentation amplifier is

illustrated in Figure 4-10. 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 4-10:

Three-Op Amp

Instrumentation Amplifier.

4.9.4

PRECISION GAIN WITH GOOD

LOAD ISOLATION

In Figure 4-11, 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 4-11:

Precision Gain with Good

Load Isolation.

MCP616

11.0 k

100 k

10 k

VDD/2

VOUT

OU T

–

() 1

------

----------

⎝⎠

⎜⎟

⎛⎞

REF

MCP617

VOUT

VREF

MCP617

OUT

–

() 1

---------

⎝⎠

⎜⎟

⎛⎞ R

------

⎝⎠

⎜⎟

⎛⎞

REF

MCP617

VREF

MCP616

MCP617

VOUT

OUT

IN 1R2 R1

⁄

()

MCP616

VOUT

VIN

MCP606

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