ICL7134 Datasheet, PDF (9/16 Pages) Intersil Corporation – 14-Bit Multiplying Microprocessor-Compatible D/A Converter

ICL7134
Definition of Terms
Nonlinearity - Error contributed by deviation of the DAC
transfer function from a straight line through the end points of
the actual plot of transfer function. Normally expressed as a
percentage of full scale range or in (sub)multiples of 1 LSB.
Resolution - It is addressing the smallest distinct analog out-
put change that a D/A converter can produce. It is commonly
expressed as the number of converter bits. A converter with
resolution of n bits can resolve output changes of 2^-n of the
full-scale range, e.g. 2^-n V_REF for a unipolar conversion. Res-
olution by no means implies linearity.
Settling Time - Time required for the output of a DAC to
settle to within specified error band around its final value
(e.g. 1/2 LSB) for a given digital input change, i.e. all digital
inputs LOW to HIGH and HIGH to LOW.
Gain Error - The difference between actual and ideal analog
output values at full-scale range, i.e., all digital inputs at
HIGH state. It is expressed as a percentage of full-scale
range or in (sub)multiples of 1 LSB.
Feedthrough Error - Error caused by capacitive coupling
from V_REF to I_OUT with all digital inputs LOW.
Output Capacitance - Capacitance from I_OUT terminal to
ground.
Output Leakage Current - Current which appears on I_OUT
terminal when all DAC register outputs are LOW.
Detailed Description
The ICL7134 consists of 14-bit primary DAC, two PROM
controlled correction DACs, input buffer registers, and
microprocessor interface logic (See Functional Block
Diagram). The 14-bit primary DAC is an R-2R thin film
resistor ladder with N-channel MOS SPDT current steering
switches. Precise balancing of the switch resistances, and
all other resistances in the ladder, results in excellent
temperature stability.
True 14-bit linearity is achieved by programming a floating poly-
silicon gate PROM array which controls two correction DAC cir-
cuits. A 6-bit gain correction DAC, or G-DAC, diverts up to 2%
of the feedback resistor’s current to Analog GND and reduces
the gain error to less than 1 LSB, or 0.006%. The 5 most
significant outputs of the DAC register address a 31-word
PROM array that controls a 12-bit linearity correction DAC, or
C-DAC. For every combination of the primary DAC’s 5 most
significant bits, a different C-DAC code is selected. This allows
correction of superposition errors, caused by bit interaction on
the primary resistor ladder’s current output bus and by voltage
non-linearity in the feedback resistor. Superposition errors can-
not be corrected by any method which corrects individual bits
only, such as laser trimming. Since the PROM programming
occurs in packaged form, it corrects for resistor shifts caused by
the thermal stresses of packaging. These packaging shifts limit
the accuracy that can be achieved using wafer level correction
methods such as laser trimming, which has also been found to
degrade the time stability of thin film resistors at the 14-bit level.
Analog Section
The ICL7134 inherently provides both unipolar and bipolar
operation. The bipolar application circuit (Figure 6) requires
one additional op-amp but no external resistors. The two on-
chip resistors, R_INV1 and R_INV2, together with the op-amp,
form a voltage inverter which drives the MSG reference ter-
minal, V_RFM, to -V_REF, where V_REF is the voltage applied at
the less significant bits’ reference terminal, V_RFL. Notice the
values of 1.95R and 2R for the R_INV1 and R_INV2. The V_RFM
absolute value is about 2.5% higher than the V_RFL. This is
necessary so that the gain error can be corrected. This
reverses the weight of the MSG, and gives the DAC a 2’s
complement transfer function. The op-amp and reference
connection to V_RFM and V_RFL can be reversed, without
affecting linearity, but a small gain error will be introduced.
For unipolar operation the V_RFM and V_RFL terminals are
both tied to V_REF, and the R_INV pin is left unconnected.
Since the PROM correction codes required are different for
bipolar and unipolar operation, the ICL7134 is available in
two different versions; the ICL7134U, which is corrected for
unipolar operation, and the ICL7134B, which is programmed
for bipolar application. The feedback resistance is also differ-
ent in the two versions, and is switched under PROM control
from ‘R’ in the unipolar device to ‘2R’ in the bipolar part.
These feedback resistors have a dummy (always ON) switch
in series to compensate for the effect of the ladder switches.
This greatly improves the gain temperature coefficient and
the power supply rejection of the device.
FIGURE 6. BIPOLAR OPERATION WITH INVERTED V_REF TO MSB
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