TLV1570 Datasheet, PDF (10/28 Pages) Texas Instruments – 2.7 V TO 5.5 V 8-CHANNEL 10-BIT 1.25-MSPS SERIAL ANALOG-TO-DIGITAL CONVERTER

TLV1570
2.7 V TO 5.5 V 8-CHANNEL 10-BIT 1.25-MSPS
SERIAL ANALOG-TO-DIGITAL CONVERTER
SLAS169A – DECEMBER 1997– REVISED SEPTEMBER 1998
simplified analog input analysis (continued)
Driving Source†
Rs
VS
TLC1570
MO
VI ^Ri(MUX)
AIN
Ri(ADC)
VC
Ci
15 pF
VI = Input Voltage at AIN
VS = External Driving Source Voltage
Rs = Source Resistance
Ri(ADC)= Input Resistance of ADC
Ri(MUX)= Input Resistance (MUX on resistance)
Ci = Input Capacitance
VC = Capacitance Charging Voltage
† _{Driving source requirements:}
• Noise and distortion for the source must be equivalent to the resolution of the converter.
• Rs must be real at the input frequency.
Figure 6. Equivalent Input Circuit Including the Driving Source
definitions of specifications and terminology
integral nonlinearity (INL)
Integral nonlinearity refers to the deviation of each individual code from a line drawn from zero through full scale.
The point used as zero occurs 1/2 LSB before the first code transition. The full scale point is defined as level
1/2 LSB beyond the last code transition. The deviation is measured from the center of each particular code to
the true straight line between these two points.
differential nonlinearity (DNL)
An ideal ADC exhibits code transitions that are exactly 1 LSB apart. DNL is the deviation from this ideal value.
A differential nonlinearity error of less than ±1 LSB ensures no missing codes.
zero offset
The major carry transition should occur when the analog input is at zero volts. Zero error is defined as the
deviation of the actual transition from that point.
gain error
The first code transition should occur at an analog value 1/2 LSB above negative full scale. The last transition
should occur at an analog value 1 1/2 LSB below the nominal full scale. Gain error is the deviation of the actual
difference between first and last code transitions and the ideal difference between first and last code transitions.
signal-to-noise ratio + distortion (SINAD)
SINAD is the ratio of the rms value of the measured input signal to the rms sum of all other spectral components
below the Nyquist frequency, including harmonics but excluding dc. The value for SINAD is expressed in
decibels.
effective number of bits (ENOB)
For a sine wave, SINAD can be expressed in terms of the number of bits. Using the following formula,
N = (SINAD – 1.76)/6.02
It is possible to get a measure of performance expressed as N, the effective number of bits. Thus, effective
number of bits for a device for sine wave inputs at a given input frequency can be calculated directly from its
measured SINAD.
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