TMC1175A
PRODUCT SPECIFICATION
Functional Description
The TMC1175A 8-bit A/D converter uses a two-step archi-
tecture to perform analog-to-digital conversion at rates up to
40 Msps. The input signal is held in an integral track/hold
stage during the conversion process. Operation is pipelined,
with one input sample taken and one output word provided
for each CONVert cycle.
The first step in the conversion process is a coarse 4-bit
quantization. This determines the range of the subsequent
fine 4-bit quantization step. To eliminate spurious codes, the
fine 4-bit A/D quantizer output is gray-coded and converted
to binary before it is combined with the coarse result to form
a complete 8-bit result.
V DDA
VR+
+2.6V
R
T
R+
324Ω
RREF
270Ω
R
B
+0.6V
Analog Input and Voltage References
The TMC1175A converts analog signals in the range R
B
to
R
T
into digital data. Input signals outside that range produce
“saturated” 00h or FFh output codes. The device will not be
damaged by signals within the range A
GND
to V
DDA
.
Input voltage range is very flexible and extends from the +5
Volt power supply to ground. Performance is specified over
the optimom 2 volt input range: 0.6V to 2.6V. However, the
part will function with a full-scale range from 1.0V to 5.0V.
A reduced input range may simplify analog signal condition-
ing circuitry, at the expense of additional noise sensitivity
and reduced differential linearity. Increasing the range can
improve differential linearity, but imposes a greater burden
on the input signal conditioning circuitry.
In many applications, external voltage reference sources are
connected to the R
T
and R
B
pins. R
B
can be grounded. Gain
and offset errors are directly related to the accuracy and sta-
bility of the applied reference voltages.
Two reference pull-up and pull-down resistors connected to
VR+ and VR– are provided internally for operation without
external voltage reference circuitry (Figure 1). The reference
voltages applied to R
T
and R
B
may be generated by connect-
ing VR+ to R
T
and VR- to R
B
. The power supply voltage is
divided by the on-chip resistors to bias the R
T
and R
B
points.
This sets-up the converter for operation in its nominal range
from 0.6V to 2.6V.
VR–
R–
81Ω
27010A
Figure 1. Reference Resistors
With V
DDA
at 5.0V, connecting VR+ to R
T
and grounding
R
B
will provide an input range from 0.0V to 2.27V, while
connecting R
T
to V
DDA
and R
B
to VR- produces a full scale
range of 3.85V referenced to V
DDA
. External resistors may
also be employed to provide arbitrary reference voltages, but
they will not match the temperature coefficient of the on-
chip resistors as well as R+ and R-, and will cause the con-
verter transfer function to vary with temperature.
With this implementation, errors in the power supply voltage
end up on the conversion data output.
Because a two-step conversion process is employed, it is
important that the references remain stable during the
ENTIRE conversion process (two clock cycles). The refer-
ence voltage can then be changed, but any conversion in
progress during a reference change is invalid.
2
REV. 1.3.3 2/28/02
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
