MCP6D11T-E datasheet(31/60 Pages) MICROCHIP

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 2019 Microchip Technology Inc.

DS20006162A-page 31

MCP6D11

“Amplifier

Configuration

Options”.

Figure 4-5

shows the typical representation of a differential I/O

amplifier with its feedback resistor network, and also

showing an equivalent circuit implementation based on

standard op amps that illustrates more clearly the

inverting amplifier configuration for the differential

signal path.

FIGURE 4-5:

Equivalent Basic Circuit Functions.

Comparing the two equivalent differential circuits of

Figure 4-5, the key difference is that in the case of the

two inverting operational amplifiers, the common-mode

voltage is controlled by the voltage applied to the

non-inverting inputs. For the differential I/O amplifier

the output common-mode voltage is controlled using

an independent feedback loop circuit (see Figure 4-1).

4.3.1

VOCM INPUT

As mentioned earlier (see Section 4.1 “Overview”),

the internal feedback control-loop drives the output

common-mode voltage (VOUT_CM) to be equal to the

voltage present at the VOCM pin. When the pin is left

open, VOCM defaults approximately to a mid-supply

voltage level set by the internal resistor divider (see

Figure 4-1).

EQUATION 4-21:

The VOCM input can be connected to an external refer-

ence voltage and varied within the specified range to

accommodate specific output common-mode levels

and achieve tighter control and higher accuracy. Refer

to Figure 3-30 and Figure 3-31 for the impact on the

achievable distortion when setting the VOCM voltage

away from mid-supply. In any case, an external decou-

pling capacitor is recommended to be added on the

VOCM pin to reduce the otherwise high output noise for

this high impedance node.

RF1

RF2

RG2

RG1

VIN-

VIN+

VOCM

VOUT+

VOUT-

RF1

RG1

VIN-

RG2

VIN+

RF2

VOCM

VOUT+

VOUT-

Equivalent

VSJ-

VSJ+

VOUT_CM

VOUT+ VOUT-



------------------------------------------------- VOCM



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