Interface Electronics

Laboratory 01/02

Group A04, ****68, G

Overview

Abstract
Download LTSPICE files from the personal pages of Hochschule Kempten
Design of Low Pass Filter with assigned parameter values for simulation and observation
Simulation of Low Pass Filter
Simulation of ADC and DAC converter
Simulation of 3 bit DAC for DNL and INL measurement
Summary
Reference

Abstract

The first and second laboratory works of Interface Electronics are based the theoretical lectures of Low Pass Filter, ADC (Analog to Digital Converter) and DAC (Digital to Analog Converter) converters.

Laboratory tasks are conducted in a simulation environment of LTSpice software. The first part was to develop and design Low Pass Filter circuit with given parameters, the second part was to simulate the

given 4 bit ADC and DAC converters and the third part is to measure DNL and INL. The main goal of these task is to give the insight of the operation of Data Converters. Furthermore, given 3 bit

DAC is simulated for DNL and INL measurements (measurement script is used) Installation and simulations are executed according to the guidelines from the personal pages of Interface Electronics

since it as guided laboratory. It should be noted the procedures differ because the computer operating system is in MacOS. Furthermore, with results of the simulation, own experience and thoughts are written.

Designing Low Pass Filter in LTSpice

Based on the first laboratory session and LTSpice page from week 2, the Low Pass Filter is designed and simulated.

The circuit design was made with parameters of R=100k, C=50n and the amplitude of sine voltage signal is 1V
Spice directives of (.op) and (.tran) for transient simulation, (.dc) for direct current and .ac for Bodeplot simulation were written.

Simulation Results of Low Pass Filter

The figure below shows the frequency response of the circuit.

It can be assumed that, if the corresponding frequency of 3dB is around 30.5 to 31 Hz which is corner frequency.

This means it will filter the signal over this value (not completely).

The figure below depicts the correlation between input and output voltages

4 Bit AD and DA Converters

For the second part fo the laboratory work, 4 bit Analog to Digital and Digital to Analog Converter is simulated and analyzed.

From the figure below, X4 represents ADC and X2 DAC

X4 has three inputs which includes clock, input 1 and voltage source and 4 digital outputs
On the DAC, X2 has clock and 4 digital inputs and one voltage output
As a analog input signal, voltage sine wave with amplitude of 1V is given.
Afterwards, by passing X4, it is digitalized in 4 bits of information
At the X2, the digital signal then converted back to analog signal (which is not a exactly same as the input analog signal)

Simulation Results of 4 Bit AD and DA Converters

Figure shows both simulation results of ADC and DAC for a comparison.

Output signal resembles input signal and close to sine wave
It can be seen that 16 steps (2^4=16) are present

Figure below depicts simulation results of ADC and DAC with lower sampling rate(10000n instead of 1n).

3 Bit DAC for DNL and INL Measurement

For the measurements for DNL and INL, a real 3 bit DAC is used with real transistors. With the measurement scripts on LTSpice

the values of output voltage are obtained.

Figure below shows output voltage characteristic of 3 bit DAC over time

Discussion

4 bit ADC and DAC converter is an example of aspect of digital signal processing. Analog signal (in this case sine wave of voltage)

is given and it then digitalized. Experiments were conducted to test under different sampling condition. It is reasoned that higher

sampling rate cause more accurate output analog signal. Moreover, another method to acquire good quality signal is to increase

the number of bits. For any kind of analog signal, finding a suitable sampling rate is crucial. If the 12 bit ADC and DAC is simulated

and analyzed, output signal is significantly closer to the input analog signal compared to 4 bit converter (file can be found under name

12Bit_ADC_DAC_pipe.asc). Furthermore, for DNL and INL measurement, real life 3 bit DAC with actual transistors is taken. By using

measurement script for every step of the voltage (since it is 3 bit 2^3=8 steps), the voltage values are attained. Afterwards,

with the values of LSB, DNL and INL for every voltage step is then calculated using the formulas from the lecture 3 and processed

on Microsoft Excel for a table and a graph of DAC transfer characteristics. Static errors are apparent due to switching operations (using

transistors. In practical situtation, these errors (DNL and INL) are present all time (acquire as close as possbile to initial analog

signal). The goal is to minimize them.

Experience During Laboratory Training

Since operating system was different (MacOS), procedures for conducting the experiments were also different (difficult).
For text editor, a program named BBEdit is used.
Writing a webpage lab report on html was an new and interesting experience (sometimes confusing). Most of the time went
to this part.
Designing a schematics on LTSpice was not difficult because of the pre-knowledge from subject of Microelectronics
Another difficulty happened when adding LTSpice file to html code. It was visible on the webpage. Furthermore, default
web browsers Chrome and Safari were not suitable for making webpages instead Firefox was installed and used.
Compared to normal way to execute the measurement script, running the measurement command was different. In order
to execute measurement script successfully, the scripts were included in the spice netlist and .log file command was selected from there.

Code(n)	V(out)	V(ideal)	DNL
0	0	0	0
1	0.39999	0.5	-2.00E-01
2	0.89863	1	-2.72E-03
3	1.54425	1.5	2.91E-01
4	2.03213	2	-2.42E-02
5	2.54601	2.5	2.78E-02
6	2.99885	3	-9.43E-02
7	3.49998	3.5	2.26E-03

Code(n)	V(out)	V(ideal)	INL
0	0	0	0
1	0.39999	0.5	-2.00E-01
2	0.89863	1	-2.03E-01
3	1.54425	1.5	8.85-02
4	2.03213	2	6.43E-02
5	2.54601	2.5	9.20E-02
6	2.99885	3	-2.30E-02
7	3.49998	3.5	-4.00E-03

2020 10 19 Interface Electronics Web report GroupA04 Gantumur