B&B Electronics SDAIBB manual Maximum Differential, Vout = in + − in − G + OutputOffset

Maximum Differential

To determine the maximum differential voltage that can be amplified, the gain and the common mode voltage must be known first. Using this information, the most positive the differential voltage may be is calculated using Equation 12. Equation 13 is used to calculate the most negative that the differential voltage may swing. These two values are still limited by the maximum allowable swing given by Equation 14.

Equation 12: VDIFF = 2(4.4 − VCM )

G

Equation 13: VDIFF = 2(VCM + 0.590V )

G

Equation 14: InputRange ≤ 4.94V G

Example: Find the allowable swing of a signal with a common mode voltage of 1V with a gain of 50.

From Equation 12:	V	DIFF		=	2(4.4 − 1)		=	0.136
					50
From Equation 13:	V	DIFF	=		2(1 +	0.590)		0.0636
						50
From Equation 14: InputRange ≤						4.94			= 0.0988
						50

The differential voltage can swing as negative as –0.0636 V and as positive as 0.136 V. However, this full range cannot be achieved with the same output offset setting due to the 0.0988 V range from Equation 14. To find the output offset voltage that allows the lower end of this range, use Equation 1 with Vout set to 0.01 V.

Vout = (IN + − IN − )G + OutputOffset

Rearranged to calculate the desired output offset it looks like this OutputOffset = Vout − VDIFF ⋅ G

Substitute in the appropriate values and solve for the output offset. OutputOffset = 0.01 − (− 0.0636) ⋅ 50 = 3.19V

14 SDAIBB1300 Manual

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