Athena III User Manual Rev A.03
www.diamondsystems.com
Page
68
16. DIGITAL-TO-ANALOG OUTPUT RANGES AND RESOLUTION
16.1
Description
Athena III 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 III computer hardware to an analog signal
terminating at an external source.
16.2
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
16.3
Output Range Selection
Jumper block J26 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 cases, 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.