TLC876M_07 Datasheet, PDF (12/22 Pages) Texas Instruments – 10-BIT 20 MSPS PARALLEL OUTPUT CMOS ANALOG-TO-DIGITAL CONVERTERS

TLC876M, TLC876I, TLC876C
10-BIT 20 MSPS PARALLEL OUTPUT CMOS
ANALOG-TO-DIGITAL CONVERTERS
SLAS140E – JULY 1997 – REVISED OCTOBER 2000
PRINCIPLES OF OPERATION
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 a 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. This parameter is sometimes referred to as linearity error.
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. This parameter is sometimes
referred to as differential error.
offset error
The first transition should occur at a level 1/2 LSB above zero. Offset is defined as the deviation of the actual
first code transition from that point.
gain error
The first code transition should occur for an analog value 1/2 LSB above nominal negative full scale (the voltage
applied to the REFBF terminal). The last transition should occur for an analog value 1 1/2 LSB below nominal
positive full scale (the voltage applied to the REFTF terminal). Gain error is the deviation of the actual difference
between the first and last code transitions from the ideal difference between the first and last code transitions.
pipeline delay (latency)
The number of clock cycles between conversion initiation on an input sample and the corresponding output data
being made available. Once the data pipeline is full, new valid output data are provided every clock cycle.
reference top/bottom offset
Resistance between the reference input and comparator input tap points causes offset errors. These errors can
be nulled out by using the force-sense connection as shown in the driving the reference terminals section.
driving the analog input
Figure 12 shows an equivalent input circuit of the TLC876 sample-and-hold amplifier and it represents an
excellent first order approximation.
The total equivalent capacitance, C_E, is typically less than 5 pF and the input source must be able to charge
or discharge this capacitance to 10-bit accuracy in the sample period of one half of a clock cycle. When the
switch S1 closes, the input source must charge or discharge the capacitor C_E from the voltage already stored
on C_E (the previously captured sample) to the new voltage. In the worst case, a full-scale voltage step on the
input, the input source must provide the charging current through the switch resistance R_SW (50 Ω) of S1 and
quickly settle (within 1/2 CLK period), and, therefore, the source is driving a low input impedance. However,
when the source voltage equals the value previously stored on C_E, the hold capacitor requires no input current
to maintain the charge and the equivalent input impedance is extremely high.
Adding series resistance between the output of the source and the AIN terminal reduces the drive requirements
placed on the source, as shown in Figure 13. To maintain the frequency performance outlined in the
specifications, the resistor should be limited to 200 Ω minus the source resistance or less. The maximum source
resistance, R_S, for 10-bit, 1/2 LSB accuracy is given by equation 1.
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