AS1545 datasheet(29/34 Pages) AMSCO

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AS1545

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

Figure 52. Reading Data from Both ADCs on One DOUT Line with 32 SCLKs

Figure 53. 32 SCLKs Data transfer for all modes in DOUTA, DOUTB

Difference calculator and quadrature signals calculator

The AS1545 internally calculates the difference between the output codes of ADC A and ADC B. There are several

requirements that need to be taken into account in order to work with the difference calculator. First off, the output data

of both ADCs needs to be in straight binary coding. This means that the difference calculator will only give the correct

results in single ended and pseudo differential modes. Also, it is important to note that in order to read the data from

the difference calculator we must read all 32 bits of data of the ADC, therefore reducing the overall sampling rate of the

ADC by half.

The difference calculator will always give you a 13 bit two’s complement result. The first bit is the sign of the operation

and the next 12 bits are the data. For simplicity in the design, an systematic error of 1 LSB can be expected from the

difference calculator.

Below we have an detailed example describing the operation of the difference calculator.

Let’s assume that VINA = 1.667V VINB = 2V VREF = 2.5V and we are working in single ended mode.

DOUT_A = 1010 1010 1010 or 2730 in decimal

DOUT_B = 1100 1100 1100 or 3276 in decimal

The difference should be 2730-3276=-546 in decimal

In 2’s complement -546 is 1 1101 1101 1110 in binary. This is a 1 for the minus sign plus 4096-546=3550 in decimal

which corresponds to 1101 1101 1110 in binary

As stated before, there is a -1LSB error in the operation so the actual output should be -547 in decimal which

corresponds to 1 1101 1101 1101 in binary which is the result that the difference calculator clocks out.

tCH

DB11A DB10A

THREE-

STATE

3 LEADING

ZEROES

THREE-

STATE

DOUTA

SCLK

CSN

tCSS

tCL

tDOH

tCSDOE

DB11B

DB0B

tDOD

1 TRAILING ZERO

3 LEADING ZEROES

1 TRAILING

ZERO

tDOV

000

SDATA_A

0+SDATA_B

000

SDATA_A

Counter + DIR + A + B

000

SDATA_A

DIF

DOUTA

CSN

DOUTA*

DOUTB

* only applicable when SGL/DIFF = 0

; Α2=1, Α1=1, Α0=0

16bit

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