TMC1103
PRODUCT SPECIFICATION
Circuit Function
Within the TMC1103 are three 8-bit A/D converters, each
employing two-step architecture to convert an analog input
to a digital output at rates up to 50 Msps. Input signals are
held in integral track/hold stages during the conversion pro-
cess. Operation is pipelined, with one input sample taken and
one output word provided for each CLK
X
cycle.
Each of the three converters function identically. In the fol-
lowing descriptions ‘X’ refers to a generic input/output or
clock where ‘X’ is equivalent to A, B or C.
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.
Analog
Input
0.1µF
V
INX
A/D Converter
V
CLPX
CLP
X
65-1103-02
Input Clamp Circuit
Digital Inputs and Outputs
Sampling of the applied input signal occurs on the falling
edge of the CLK
X
signal (Figure 1). Output data is delayed
by 2 1/2 CLK
X
cycles and is valid following the rising edge
of CLK
X
. Previous output data remains valid for t
HO
(Out-
put Hold Time). New data becomes valid t
D
(Output Delay
Time) after this rising edge of CLK
X
.
Whenever the analog input signal is sampled and found to be
at a level beyond the A/D conversion range, the output limits
at 00h or FFh, as appropriate.
Analog Input and Voltage References
Each A/D accepts analog signals in the range R
BX
to R
TX
into
digital data. Input signals outside this range produce “satu-
rated” 00h or FFh output codes. The device will not
be damaged by signals within the range A
GND
to V
DDA
.
Input range is very flexible and extends from the +5 Volt
power supply to ground. Nominal input range is 2 Volts,
extending from 0.6V to 2.6V. Characterization and
performance is specified over this range. However, the
part will function with a full-scale range from 1.0V to 5.0V.
A smaller input range may simplify analog signal condition-
ing circuitry, at the expense of additional noise sensitivity
and some reduced differential linearity performance.
External voltage reference sources are connected to the R
TX
and R
BX
pins. R
BX
can be grounded. Within each A/D con-
verter is a reference resistor ladder comprising 255 resistors
that are accessed by the TMC1103 comparators. R
TX
is con-
nected to the top of the ladder, R
BX
to the bottom. Gain and
offset errors are directly related to the accuracy and stability
of the applied reference voltages.
Table 1. A/D Output Coding
Input Voltage
R
TX
+ 1 LSB
R
TX
R
TX
- 1 LSB
•••
R
BX
+ 128 LSB
R
BX
+ 127 LSB
•••
R
BX
+ 1 LSB
R
BX
R
BX
- 1 LSB
Note:
1 LSB = (R
TX
– R
BX
) / 255
Output
FF
FF
FE
•••
80
7F
•••
01
00
00
Input Clamps
A clamp circuit is connected to the input pin V
INX
of each of
the three A/D converters. With CLP
X
LOW, the input pin is
clamped to the voltage at V
CLPX
. If CLP
X
is HIGH, the
input pin is high impedance. Clamping adds an offset voltage
to an AC coupled signal to adjust this signal’s amplitude to
the A/D converter input voltage range.
The analog input is corrected through a 0.1mF capacitor to
V
INX
. The source impedance of the analog source should be
less than 50 Ohms. Current pulses through the capacitor over
several clamp cycles until the voltage across the capacitor
equals the difference between V
CLPX
and the voltage at the
analog source during the clamping period. When the switch
is open, the voltage on the coupling capacitor is added to the
analog input, producing a a DC offset input signal.
The outputs of the TMC1103 are CMOS- and
TTL-compatible, and are capable of driving four low-power
Schottky TTL loads. An Output Enable control, OE
X
, places
the A/D outputs in a high-impedance state when HIGH.
The outputs are enabled when OE
X
is LOW.
Power and Ground
The TMC1103 operates from a single +5 Volt power supply.
For optimum performance, an analog ground plane should
be placed under the TMC1103 the A
GND
and D
GND
pins
should be connected to the system analog ground plane.
2
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
