DE10-Standard
User Manual
85
www.terasic.com
January 19, 2017
Figure
5
-21 LTC2308 Timing with a Short CONVST Pulse
Important: Users should pay more attention to the impedance matching between the input source
and the ADC circuit. If the source impedance of the driving circuit is low, the ADC inputs can be
driven directly. Otherwise, more acquisition time should be allowed for a source with higher
impedance.
To modify acquisition time tACQ, user can change the tHCONVST macro value in adc_ltc2308.v.
When SCK is set to 40MHz, it means 25ns per unit. The default tHCONVST is set to 320,
achieving a 100KHz fsample. Thus adding more tHCONVST time (by increasing tHCONVST
macro value) will lower the sample rate of the ADC Converter.
`define tHCONVST
320
Figure 5-22
shows the example MUX configurations of ADC. In this demonstration, it is
configured as 8 signal-end channel in the verilog code. User can change SW[2:0] to measure the
corresponding channel.The default reference voltage is 4.096V.
The formula of the sample voltage is:
Sample Voltage = ADC Data / full scale Data * Reference Voltage.
In this demonstration, full scale is 2^12 =4096. Reference Voltage is 4.096V. Thus
ADC Value = ADC data/4096*4.096 = ADC data /1000