Hochschule Kempten      
Fakultät Elektrotechnik      
Interface Electronics       Fachgebiet Elektronik, Prof. Vollrath      

Interface Electronics

Laboratory 02: LTSPICE DAC analysis instructions

Prof. Jörg Vollrath

Start 10.11.2025


Overview

This is a laboratory to simulate unit element and binary weighted DAC errors.

8 Bit ADC DAC Test Starting Point


The schematic shows a 8-bit ADC DAC System.
Download the circuit.
This is the starting point for this laboratory.

R2R DAC Schematic


The schematic shows a 8-bit R2R DAC.
Download the circuit.
Add it to the 8 Bit ADC DAC set up.
Simulate a ramp test and a sine test.
Change resistance +10%, -10%.
R13 Grp1, R12 Grp3, R11 Grp 5, R10 Grp 7, R9 Grp 9.
Extract the simulated values with Read Raw File .
Document and discuss INL and DNL values.

Simulate a sine signal test.
Extract the simulated values with Read Raw File .
Calculate FFT values.
Document and discuss FFT, INL, DNL and SNR values.

Please submit via email to joerg.vollrath@hs-kempten.de until 1.12.2025 a report covering this laboratory.



R-Ladder Interpolating DAC Schematic


The schematic shows a 8-bit R2R DAC.
Download the circuit.
Add it to the 8 Bit ADC DAC set up.
Simulate a ramp test and a sine test.
Change resistance in subcircuit 4Bit_RLadder_DAC_Scale +10%, -10%.
R13 Grp2, R11 Grp4, R9 Grp6, R15 Grp 8, R6 Grp 10.
Extract the simulated values with Read Raw File .
Document and discuss INL and DNL values.

Simulate a sine signal test.
Extract the simulated values with Read Raw File .
Calculate FFT values.
Document and discuss FFT, INL, DNL and SNR values.

Please submit via email to joerg.vollrath@hs-kempten.de until 1.12.2025 a report covering this laboratory.



Video Instructions LTSPICE ADC DAC Test Circuit

This video presents the download and run of LTSPICE files.
Search for "Vollrath InEl"
Open LTSPICE presentation.
Go to "Scalable behavioral 4 Bit DAC", "Scalable behavioral 4 Bit ADC", "Test for 4 Bit ADC and DAC" slides and download circuits (.asc) and (.asy) presented to you after clicking on the circuit.
Run the sine simulation and view V(in1),V(out).
Create a pulse voltage source:
V1 in1 0 PULSE(0 1 0 655.36u 655.36u 0 1310.72u)
Run a ramp simulation.
Duration 10:52 min

01:20: : Download schematics for schematics
04:10: : Download symbols for 4Bit_ADC_DAC_pipe.asc, 4Bit_ADC_pipe.asc, 4Bit_DAC_pipe.asc, sample_hold.asc, Switch.asc,WS2011_Prob4.asc
05:00: : Sine input
05:35: : Output signal
06:30: : LTSPICE FFT
07:30: : Ramp
09:35: : Voltage source

Video Instructions LTSPICE INL, DNL FFT Analysis

This video presents the analysis of LTSPICE simulation files.
Run the ADC DAC test simulation in LTSPICE with a ramp.
Extract the simulated values with Read Raw File .
Use analysis buttons to:
  • Show extracted values
  • Map values to integers
  • DAC INL, DNL analysis
  • ADC histogram analysis
Run the ADC DAC test simulation in LTSPICE with a sine signal.
Extract the simulated values with Read Raw File .
Use the integer values for a FFT analysis.

How can you extract only less 16*1024 values?
Describe the changes in the FFT results?
Duration 13:48 min

00:28: : Read LTSPICE raw data
04:15: : Start time 0, Stop time 655.36E-6, Time step: 40.96E-6
04:58: : First data
05:50: : Map to integer
06:25: : DNL INL graph
07:13: : Histogram with smaller step size 5.12E-6
08:10: : Map to integer
08:42: : ADC histogram analysis
09:20: : Simulate sine
09:50: : Read data values
11:05: : Histogramm test
11:40: : Copy values
12:00: : ADC FFT Javascript, Fill input data field, read integer values
12:50: : SNR 11.87-(-13.89) dB = 25.76 dB  ENOB = (15.76-1.76)/6.02 = 4
13:16: : Sine histogram INL and DNL

Simulation R2R DAC


The schematic shows a 4-bit R2R DAC.
We will use it in the ADC DAC simulation to see some errors.
Create a symbol and hook it up to the ADC DAC test circuit from last week.
Modify the resistance values. For example 1.5k, 2.5k, 1.3k, 1.7k.
Simulate a ramp test.
Extract the simulated values with Read Raw File .
Calculate INL, DNL with any tool. Document and discuss INL and DNL values.

Simulate a sine signal test.
Extract the simulated values with Read Raw File .
Calculate FFT, INL, DNL with FFT webpage and paste the extracted values from LTSPICE into the input field.
Document and discuss FFT, INL, DNL and SNR values.
Duration 6:34 min

00:34: : Include R2R DAC
01:52: : Simulate real R2R DAC
02:23: : Modify R values: R6 1.3k, R9 1.5k
03:16: : Read, mapto integer, copy values to FFT, process
04:29: : SNR 12.09-(-6.75) dB = 18.84 dB
04:55: : Ramp test
05:28: : Step 40.96E-6
06:07: : INL and DNL with error

Video Instructions LTSPICE .Measurement

This video presents the analysis of LTSPICE simulation files with a .measure statement.
Run the ADC DAC test simulation in LTSPICE with a ramp.
Insert SPICE directive:
.meas trans OUT00 FIND V(vout) AT=81.92us
After simulation "View","SPICE Error log" will show the result.
Multiple measurement statements can be placed into a file.
After simulation "File","Execute .MEAS script" generates the results.
A 10-bit data converter should have about 16384 measurement values. Data extraction can be difficult and quite time consuming.
Duration 5:55 min

00:44: Measurement statement
01:35: First measurement statement: .meas trans OUT00 FIND V(vout) at t=20.48u
05:20: .meas script