AD976/AD976A
PIN FUNCTION DESCRIPTIONS
Pin No.
Mnemonic
Description
1
VIN
Analog Input. Connect a 200 Ω resistor between VIN and the analog signal source. The full-scale
input range is ±10 V.
2
3
AGND1
REF
Analog Ground. Used as the ground reference point for the REF pin.
Reference Input/Output. The internal +2.5 V reference is available at this pin. Alternatively, an
external reference can be used to override the internal reference. In either case, connect a 2.2 µF
tantalum capacitor between REF and AGND1.
4
5
6
CAP
Reference Buffer Output. Connect a 2.2 µF tantalum capacitor between CAP and AGND2.
AGND2
D15 (MSB)
Analog Ground.
Data Bit 15. Most significant bit of conversion result. High impedance state when CS is HIGH or
when R/C is LOW.
7–13
14
D14–D8
DGND
Data Bits 14–8. High impedance state when CS is HIGH or when R/C is LOW.
Digital Ground.
15–21
22
D7–D1
Data Bits 7–1. High impedance state when CS is HIGH or when R/C is LOW.
D0 (LSB)
Data Bit 0. Least significant bit of conversion result. High impedance state when CS is HIGH or
when R/C is LOW.
23
BYTE
Byte Select. With BYTE LOW, data will be output as indicated above; Pin 6 (D15) is the MSB,
Pin 22 (D0) is the LSB. With BYTE HIGH, the top and bottom 8 bits of data will be switched;
D15–D8 are output on Pins 15–22 and D7–D0 are output on Pins 6–13.
24
25
R/C
Read/Convert Input. With CS LOW, a falling edge on R/C puts the internal sample/hold into the
hold state and starts a conversion; a rising edge enables the output data bits.
CS
Chip Select Input. Internally OR’d with R/C. With R/C LOW, a falling edge on CS will initiate a
conversion. With R/C HIGH, a falling edge on CS will enable the output data bits. When CS is
HIGH, the output data bits will be in the Hi-impedance state.
26
BUSY
Busy Output. Goes LOW when a conversion is started and remains LOW until the conversion is
completed and the data is latched into the output register. With CS tied LOW and R/C HIGH,
output data will be valid when BUSY rises. The rising edge of BUSY can be used to latch the out-
put data.
27
28
VANA
VDIG
Analog Power Supply. Nominally +5 V.
Digital Power Supply. Nominally +5 V.
DEFINITION OF SPECIFICATIONS
INTEGRAL NONLINEARITY ERROR (INL)
BIPOLAR ZERO ERROR
Linearity error refers to the deviation of each individual code
from a line drawn from “negative full scale” to “positive full
scale.” The point used as negative full scale occurs 1/2 LSB
before the first code transition. Positive full scale is defined as a
level 1 1/2 LSB beyond the last code transition. The deviation is
measured from the middle of each particular code to the true
straight line.
Bipolar zero error is the difference between the ideal midscale
input voltage (0 V) and the actual voltage producing the midscale
output code.
INPUT BANDWIDTH
The input bandwidth is that frequency at which the amplitude
of the reconstructed fundamental is reduced by 3 dB for a full-
scale input.
DIFFERENTIAL NONLINEARITY ERROR (DNL)
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing
codes are guaranteed.
FULL-POWER BANDWIDTH
Full-power bandwidth is defined as the full-scale input fre-
quency at which signal to (Noise + Distortion) degrades to
60 dB, as 10 bits of accuracy.
؎ FULL-SCALE ERROR
APERTURE DELAY
The last + transition (from 011. . .10 to 011. . .11) should
occur for an analog voltage 1 1/2 LSB below the nominal full
scale (9.9995422 V for a ±10 V range). The full-scale error is
the deviation of the actual level of the last transition from the
ideal level.
Aperture delay is a measure of the Sample-and-Hold Amplifier
(SHA) performance and is measured from the rising edge of the
clock input to when the input signal is held for a conversion.
REV. C
–6–
ADI [ ADI ]
