AD7856KR-REEL Analog Devices Inc, AD7856KR-REEL Datasheet - Page 8

• Manufacturer Part Number: AD7856KR-REEL
• Description: IC ADC 14BIT 8CH 5V 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD7856KR-REEL

• Rohs Status: RoHS non-compliant
• Number Of Bits: 14
• Sampling Rate (per Second): 285k
• Data Interface: 8051, QSPI™, Serial, SPI™ µP
• Number Of Converters: 2
• Power Dissipation (max): 89.25mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: 0°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)

AD7856
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The end-
points of the transfer function are zero scale, a point 1/2 LSB
below the first code transition, and full scale, a point 1/2 LSB
above the last code transition.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Total Unadjusted Error
This is the deviation of the actual code from the ideal code
taking all errors into account (Gain, Offset, Integral Nonlinearity
and other errors) at any point along the transfer function.
Unipolar Offset Error
This is the deviation of the first code transition (00 . . . 000 to
00 . . . 001) from the ideal AIN(+) voltage (AIN(–) + 1/2 LSB).
Positive Full-Scale Error
This is the deviation of the last code transition from the ideal
AIN(+) voltage (AIN(–) + Full Scale – 1.5 LSB) after the offset
error has been adjusted out.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of crosstalk between
the channels. It is measured by applying a full-scale 25 kHz
signal to the other seven channels and determining how much
that signal is attenuated in the channel of interest. The figure
given is the worst case for all channels.
Track/Hold Acquisition Time
The track/hold amplifier returns into track mode and the end of
conversion. Track/Hold acquisition time is the time required for
the output of the track/hold amplifier to reach its final value,
within 1/2 LSB, after the end of conversion.
Signal to (Noise + Distortion) Ratio
This is the measured ratio of signal to (noise + distortion) at the
output of the A/D converter. The signal is the rms amplitude of
the fundamental. Noise is the sum of all nonfundamental signals
up to half the sampling frequency (f
is dependent on the number of quantization levels in the digiti-
zation process; the more levels, the smaller the quantization
noise. The theoretical signal to (noise + distortion) ratio for an
ideal N-bit converter with a sine wave input is given by:
Thus for a 14-bit converter, this is 86 dB.
NOTE
1
AIN(+) refers to the positive input of the pseudo-differential pair, and AIN(–)
refers to the negative analog input of the pseudo-differential pair or to AGND
depending on the channel configuration.
Signal to (Noise + Distortion) = (6.02 N + 1.76) dB
1
S
/2), excluding dc. The ratio
–8–
Total Harmonic Distortion
Total Harmonic Distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7856, it is defined as:
where V
V
sixth harmonics.
Peak Harmonic or Spurious Noise
Peak harmonic or spurious noise is defined as the ratio of the
rms value of the next largest component in the ADC output
spectrum (up to f
fundamental. Normally, the value of this specification is deter-
mined by the largest harmonic in the spectrum, but for parts
where the harmonics are buried in the noise floor, it will be a
noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities will create distortion
products at sum and difference frequencies of mfa
m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are
those for which neither m nor n are equal to zero. For example,
the second order terms include (fa + fb) and (fa – fb), while the
third order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and
(fa – 2fb).
Testing is performed using the CCIF standard where two input
frequencies near the top end of the input bandwidth are used. In
this case, the second order terms are usually distanced in fre-
quency from the original sine waves, while the third order terms
are usually at a frequency close to the input frequencies. As a
result, the second and third order terms are specified separately.
The calculation of the intermodulation distortion is as per the
THD specification where it is the ratio of the rms sum of the
individual distortion products to the rms amplitude of the sum
of the fundamentals expressed in dBs.
Full Power Bandwidth
The Full Power Bandwidth (FPBW) of the AD7856 is that
frequency at which the amplitude of the reconstructed (using
FFTs) fundamental (neglecting harmonics and SNR) is reduced
by 3 dB for a full-scale input.
4
, V
5
and V
THD (dB) 20 log
1
is the rms amplitude of the fundamental and V
6
are the rms amplitudes of the second through the
S
/2 and excluding dc) to the rms value of the
V
2
2
V
3
2
V
V
1
4
2
V
5
2
V
nfb where
6
2
REV. A
2
, V
3
,