
TMC1203
PRODUCT SPECIFICATION
2
Circuit Function
Within the TMC1203 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 and Voltage References
Each A/D accepts analog signals in the range R
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
BX
 to R
TX
 into 
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
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 TMC1203 comparators. R
nected to the top of the ladder, R
offset errors are directly related to the accuracy and stability 
of the applied reference voltages.
TX
TX
 is con-
BX
 to the bottom. Gain and 
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.
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
(Output Hold Time), satisfying any hold time requirement of 
the receiving circuit. New data becomes valid t
Delay Time) after this rising edge of CLK
HO
D
 (Output 
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.
Table 1. A/D Output Coding
Note:
 1 LSB = (R
TX
 - R
BX
) / 255
The outputs of the TMC1203 are CMOS- and 
TTL-compatible, and are capable of driving four low-power 
Schottky TTL loads. An Output Enable control, OE
the A/D outputs in a high-impedance state when HIGH. 
The outputs are enabled when OE
X
, places 
X
 is LOW.
Power and Ground
The TMC1203 operates from a single +5 Volt power supply. 
For optimum performance, it is recommended that A
and D
GND
 pins of the TMC1203 be connected to the system 
analog ground plane.
GND
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
Output
FF
FF
FE
  
80
7F
  
01
00
00