REV. D

AD7711A

–8–

Pin

Mnemonic

Function

19

TFS

Transmit Frame Synchronization. Active low logic input used to write serial data to the device with serial data

expected after the falling edge of this pulse. In the self-clocking mode, the serial clock becomes active after

TFS goes low. In the external clocking mode, TFS must go low before the first bit of the data-word is written

to the part.

20

RFS

Receive Frame Synchronization. Active low logic input used to access serial data from the device. In the

self-clocking mode, both the SCLK and SDATA lines become active after

RFS goes low. In the external

clocking mode, the SDATA line becomes active after

RFS goes low.

21

DRDY

Logic Output. A falling edge indicates that a new output word is available for transmission. The

DRDY pin

will return high upon completion of transmission of a full output word.

DRDY is also used to indicate when

the AD7711A has completed its on-chip calibration sequence.

22

SDATA

Serial Data. Input/output with serial data being written to either the control register or the calibration

registers and serial data being accessed from the control register, calibration registers, or the data register.

During an output data read operation, serial data becomes active after

RFS goes low (provided DRDY is low).

During a write operation, valid serial data is expected on the rising edges of SCLK when

TFS is low. The

output data coding is natural binary for unipolar inputs and offset binary for bipolar inputs.

23

24

DGND

Ground Reference Point for Digital Circuitry.

TERMINOLOGY

Integral Nonlinearity

This is the maximum deviation of any code from a straight line

passing through the endpoints of the transfer function. The end-

points of the transfer function are zero scale (not to be confused

with bipolar zero), a point 0.5 LSB below the first code transition

(000 . . . 000 to 000 . . . 001) and full scale, a point 0.5 LSB

above the last code transition (111 . . . 110 to 111 . . . 111). The

error is expressed as a percentage of full scale.

Positive Full-Scale Error

Positive full-scale error is the deviation of the last code transi-

tion (111 . . . 110 to 111 . . . 111) from the ideal AIN(+) voltage

and bipolar analog input ranges.

Unipolar Offset Error

Unipolar offset error is the deviation of the first code transition

from the ideal AIN(+) voltage (AIN(–) + 0.5 LSB) when oper-

ating in the unipolar mode.

Bipolar Zero Error

This is the deviation of the midscale transition (0111 . . . 111

to 1000 . . . 000) from the ideal AIN(+) voltage (AIN(–)

– 0.5 LSB) when operating in the bipolar mode.

Bipolar Negative Full-Scale Error

This is the deviation of the first code transition from the ideal

ing in the bipolar mode.

Positive Full-Scale Overrange

Positive full-scale overrange is the amount of overhead available

to handle input voltages on AIN(+) input greater than AIN(–) +

system gain errors in system calibration routines) without intro-

ducing errors due to overloading the analog modulator or over-

flowing the digital filter.

Negative Full-Scale Overrange

This is the amount of overhead available to handle voltages on

analog modulator or overflowing the digital filter. Note that the

analog input will accept negative voltage peaks even in the uni-

polar mode provided that AIN(+) is greater than AIN(–) and

Offset Calibration Range

In the system calibration modes, the AD7711A calibrates its

offset with respect to the analog input. The offset calibration

range specification defines the range of voltages that the

AD7711A can accept and still accurately calibrate offset.

Full-Scale Calibration Range

This is the range of voltages that the AD7711A can accept in

the system calibration mode and still correctly calibrate full scale.

Input Span

In system calibration schemes, two voltages applied in sequence

to the AD7711A’s analog input define the analog input range.

The input span specification defines the minimum and maxi-

mum input voltages from zero scale to full scale that the AD7711A

can accept and still calibrate accurately gain.