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AS1545

Data Sheet - D e t a i l e d D e s c r i p t i o n

Figure 38. Definition of Fully Differential Input

Pseudo Differential Mode

The AS1545 consists of six pseudo differential pairs. In pseudo differential mode, AIN+ is connected to the signal

of the part. A dc input is applied to the AIN- pin. The voltage applied to this input provides an offset from ground or a

pseudo ground for the AIN+ input. The benefit of pseudo differential inputs is that they separate the analog input signal

ground from the ADC’s ground allowing dc common-mode voltages to be cancelled. Figure 39 shows a connection

diagram for pseudo differential mode.

Figure 39. Pseudo Differential Mode Connection Diagram

Figure 40. Definition of Pseudo Differential Input

VCM

AIN+

AIN-

±VREF/2

0 < VCM < VDD

0 < AIN-, AIN+ < VDD

VCM

AIN+

AIN-

±VREF

0 < VCM < VDD

0 < AIN-, AIN+ < VDD

RANGE = 0

RANGE = 1

VIN

VIN

tt

+

-

VIN+

4.7µF

DC Input Voltage

VIN-

REFA/

REFB

AS1545

VREF p-p

AIN- + VREF

AIN+

AIN-

0 < AIN-, AIN+ < VDD

0 < AIN-, AIN+ < VDD

RANGE = 0

RANGE = 1

AIN- + 2VREF

AIN+

AIN-

VREF

VIN

VIN

tt

2VREF