Digital-to-Analog Output Ranges and Resolution
Description
Athena II uses a 4-channel 12-bit D/A converter (DAC) to provide four analog outputs. A 12-bit DAC can generate
output voltages with the precision of a 12-bit binary number. The maximum value of a 12-bit binary number is 2
12
-
1, or 4095, so the full range of numerical values that the DACs support is 0 - 4095. The value 0 always corresponds
to the lowest voltage in the output range, and the value 4095 always corresponds to the highest voltage minus 1
LSB. The theoretical top end of the range corresponds to an output code of 4096 which is impossible to achieve.
Note: In this manual, the terms analog output, D/A, and DAC are all used interchangeably to mean
the conversion of digital data originating from the Athena II computer hardware to an analog signal
terminating at an external source.
Resolution
The resolution is the smallest possible change in output voltage. For a 12-bit DAC the resolution is 1/(2
12
), or
1/4096, of the full-scale output range. This smallest change results from an increase or decrease of 1 in the D/A
code, so this change is referred to as 1 least significant bit (1 LSB ). The value of this LSB is calculated as follows.
1 LSB = Output voltage range / 4096
Example:
For, Output range = 0-10V,
Output voltage range = 10V – 0V = 10V
Therefore,
1 LSB = 10V / 4096 = 2.44mV
Example:
For, Output range =
±
10V;
Output voltage range = 10V – (-10V) = 20V
Therefore,
1 LSB = 20V / 4096 = 4.88mV
Output Range Selection
Jumper block J13 is used to select the DAC output range. The DACs can be configured for 0-10V or
±
10V.
Two parameters are configured
•
unipolar/bipolar mode
•
power-up/reset clear mode.
In most case, for unipolar mode configure the board to reset to zero scale, and for bipolar mode configure the board
for reset to mid-scale. In each case the DACs reset to 0V.
D/A Conversion Formulas and Tables
Diamond Systems Corporation
Athena II User Manual
Page 77
