Data Sheet

ADA4930-1/ADA4930-2

Rev. C | Page 21 of 25

Terminating a Single-Ended Input in a Single-Supply

Applications

When the application circuit of Figure 50 is powered by a single

common-mode range. Two methods are available: a dc bias on

the source, as shown in Figure 51, or by connecting resistors

Input Common-Mode Adjustment with DC Biased Source

minimizes the power dissipation of the ADA4930-1/ADA4930-2.

The application circuit of Figure 50 on a 3.3 V single supply with a

dc bias added to the source is shown in Figure 51.

ADA4930

1.990V p-p

3.3V

50Ω

142Ω

142Ω

301Ω

301Ω

2V p-p

64.2

Ω

64.2

Ω

50

Ω

Figure 51. Single-Supply, Terminated Single-Ended-to-Differential System

with G = 1

To determine the minimum required dc bias, the following steps

must be taken:

1. Convert the terminated inputs to their Thevenin equivalents,

as shown in the Figure 52 circuit.

ADA4930

1.99V p-p

3.3V

VON

VOP

28.11Ω

142Ω

142Ω

301Ω

301Ω

1.124V p-p

28.11Ω

Figure 52. Thevenin Equivalent of Single-Supply Application Circuit

(

)

TH

DC

TH

ON

TH

DC

TH

P

V

V

V

V

V

V

−

−

−

−

+

+

+

+

+

=

28.11

142

301

28.11

142

)

(

28.11

142

301

28.11

142

TH

DC

OP

TH

DC

N

V

V

V

V

−

−

−

+

+

+

+

=

Recognize that while the ADA4930-1/ADA4930-2 is in its

both equations in Step 2 give equal results.

3. To comply with the minimum specified input common-mode

maximum).

Let

Or

5. Converting VDC-TH from its Thevenin equivalent results in

V

0.33

0.186 =

×

+

=

TH

TH

S

DC

R

R

R

V

The final application circuit is shown in Figure 53. The

additional dc bias of 0.33 V at the inputs ensures that the

minimum input common-mode requirements are met when

the source signal is bipolar with a 2 V p-p amplitude and

3.3V

ADA4930

1.990V p-p

50Ω

142Ω

142Ω

301Ω

301Ω

2V p-p

64.2Ω

64.2Ω

50

Ω

0.33V

Figure 53. Single-Supply Application Circuit with DC Source Bias