AD7819 Analog Devices, AD7819 Datasheet - Page 5

• Manufacturer Part Number: AD7819
• Description: +2.7 V to +5.5 V, 200 kSPS 8-Bit Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7819

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Par
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

TERMINOLOGY
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 rms sum of all nonfundamental
signals up to half the sampling frequency (f
The ratio is dependent upon the number of quantization levels
in the digitization process; the more levels, the smaller the quan-
tization noise. The theoretical signal to (noise + distortion)
ratio for an ideal N-bit converter with a sine wave input is given
by:
Thus for an 8-bit converter, this is 50 dB.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7819 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 ± nfb where
m, n = 0, 1, 2, 3, etc. Intermodulation 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).
4
, V
5
and V
Signal to (Noise + Distortion) = (6.02N + 1.76) dB
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
S
+ V
/2), excluding dc.
5
2
+ V
6
2
2
, V
3
,
The AD7819 is tested using the CCIF standard, where two
input frequencies near the top end of the input bandwidth are
used. In this case, the second and third order terms are of different
significance. The second order terms are usually distanced in
frequency 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 sepa-
rately. 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 fundamental expressed in dBs.
Relative Accuracy
Relative accuracy or endpoint nonlinearity is the maximum
deviation from a straight line passing through the endpoints of
the ADC transfer function.
Differential Nonlinearity
This is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (0000 . . . 000)
to (0000 . . . 001) from the ideal, i.e., AGND + 1 LSB.
Offset Error Match
This is the difference in Offset Error between any two channels.
Gain Error
This is the deviation of the last code transition (1111 . . . 110)
to (1111 . . . 111) from the ideal, i.e., VREF – 1 LSB, after the
offset error has been adjusted out.
Gain Error Match
This is the difference in Gain Error between any two channels.
Track/Hold Acquisition Time
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 (the point at which the
track/hold returns to track mode). It also applies to situations
where a change in the selected input channel takes place or
where there is a step input change on the input voltage applied
to the selected V
must wait for the duration of the track/hold acquisition time
after the end of conversion or after a step input change to V
before starting another conversion, to ensure that the part
operates to specification.
IN
input of the AD7819. It means that the user
AD7819
IN