VCM (V)

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

-80

-60

-40

-20

0

20

40

60

D005

AMC1306x25

AMC1306x05

G

R4

E (%)

1

100%

R4 ' R3 '

§

·

u

¨

¸

©

¹

32

AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25

SBAS734C – MARCH 2017 – REVISED JANAURY 2020

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Product Folder Links: AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25

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This additional series resistor (R3') influences the gain error of the circuit. The effect can be calculated using

Equation 5 with R5 = R5' = 50 kΩ and R4 = R4' = 2.5 kΩ (for the AMC1306x05) or 12.5 kΩ (for the

AMC1306x25).

(5)

9.2.2.3 Application Curve

Figure 60 shows the dependency of the input bias current on the common-mode voltage at the input of the

AMC1306.

Figure 60. Input Bias Current vs Common-Mode Input Voltage

9.2.3 What To Do and What Not To Do

Do not leave the inputs of the AMC1306 unconnected (floating) when the device is powered up. If both modulator

inputs are left floating, the input bias current drives these inputs to the output common-mode of the analog front-

end of approximately 1.9 V. If that voltage is above the specified input common-mode range, the front gain

diminishes and the modulator outputs a bitstream resembling a zero input differential voltage.