MCP6V06T datasheet(27/44 Pages) MICROCHIP

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DS22093B-page 27

MCP6V06/7/8

4.3.9.3

Difference Amplifier Layout for

Thermo-junctions

Figure 4-12 shows the recommended difference ampli-

fier circuit. Usually, we choose R1 =R2 and R3 =R4.

The guard traces (with ground vias at the ends) help

minimize the thermal gradients. The resistor layout

cancels the resistor thermal voltages, assuming the

temperature gradient is constant near the resistors:

EQUATION 4-3:

FIGURE 4-12:

PCB Layout and Schematic

for Single Difference Amplifier.

4.3.9.4

Dual Non-inverting Amplifier Layout

for Thermo-junctions

The dual op amp amplifiers shown in Figure 4-16 and

Figure 4-17 produce a non-inverting difference gain

greater than 1, and a common mode gain of 1 .They

can use the layout shown in Figure 4-13. The gain set-

ting resistors (R2) between the two sides are not com-

bined so that the thermal voltages can be canceled.

The guard traces (with ground vias at the ends) help

minimize the thermal gradients. The resistor layout

cancels the resistor thermal voltages, assuming the

temperature gradient is constant near the resistors:

EQUATION 4-4:

FIGURE 4-13:

PCB Layout and Schematic

for Dual Non-inverting Amplifier.

Note:

Changing the orientation of the resistors

will usually cause a significant decrease in

the cancellation of the thermal voltages.

VOUT ≈ VREF +(VP –VM)GDM

Where:

Thermal voltages are approximately equal

GDM

=R3/R1 =R4/R2, difference gain

VOS is neglected

VOUT ≈ VREF +(VP –VM)GDM

VOUT

MCP6V06

VREF

VOUT

VREF

Note:

Changing the orientation of the resistors

will usually cause a significant decrease in

the cancellation of the thermal voltages.

(VOA –VOB) ≈ (VIA –VIB)GDM

(VOA +VOB)/2 ≈ (VIA +VIB)/2

Where:

Thermal voltages are approximately equal

GDM =1 + R3/R2, differential mode gain

GCM = 1, common mode gain

VOS is neglected

VIB

VOA

VOB

VIA

VIB

VOB

½MCP6V07

VIA

VOA

½MCP6V07

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