MCP6271 datasheet(13/34 Pages) MICROCHIP

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 2004 Microchip Technology Inc.

DS21810D-page 13

MCP6271/2/3/4/5

FIGURE 4-6:

Example Guard Ring Layout

for Inverting Gain.

For

Inverting

Gain

and

Transimpedance

Amplifiers (convert current to voltage, such as

photo detectors):

Connect the guard ring to the non-inverting

input pin (VIN+). This biases the guard ring

to the same reference voltage as the op

amp (e.g., VDD/2 or ground).

Connect the inverting pin (VIN–) to the input

with a wire that does not touch the PCB

surface.

Non-inverting Gain and Unity-Gain Buffer:

Connect the non-inverting pin (VIN+) to the

input with a wire that does not touch the

PCB surface.

Connect the guard ring to the inverting input

pin (VIN–). This biases the guard ring to the

common mode input voltage.

4.8

Application Circuits

4.8.1

ACTIVE FULL-WAVE RECTIFIER

The MCP6271/2/3/4/5 family of amplifiers can be used

in applications such as an Active Full-Wave Rectifier or

an Absolute Value circuit, as shown in Figure 4-7. The

amplifier and feedback loops in this active voltage

rectifier circuit eliminate the diode drop problem that

exists in a passive voltage rectifier. This circuit behaves

as a follower (the output follows the input) as long as

the input signal is more positive than the reference

voltage. If the input signal is more negative than the

reference voltage, however, the circuit behaves as an

inverting amplifier. Therefore, the output voltage will

always be above the reference voltage, regardless of

the input signal.

FIGURE 4-7:

Active Full-wave Rectifier.

The design equations give a gain of ±1 from VIN to

VOUT, and produce rail-to-rail outputs.

Guard Ring

VSS

VIN–VIN+

–

VIN

VOUT

VREF

Op Amp A

Op Amp B

VREF

time

Input

Output

2R4

------------

1/2

MCP6272

1/2

MCP6272

REF

–

----------------------------

–





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