ridwan.chendarma.com

ADC DAC 2 MSPS Implementation

Implemented ADC DAC 2 MSPS on Virtex II Pro FPGA. This is a 10 times higher in sampling rate compare to the previous post ADC DAC. The sampling rate is 2 MSPS and can go up to 4 MSPS.

So by using System Generator and a verilog blackbox I implemented an FIR high-pass filter and the result is very clean. high_pass_filter_scope_captures

Add comment May 12th, 2009

Microcontroller App. Freq and Period Measurements

A simple app. using PIC18F4520 to display frequency and period measurement of an analog square wave input. Code is written in C, interrupts and internal timer1 are utilized. Display is on 2 lined LCD screen.

Schematic:

Add comment March 18th, 2009

DSB-SC Modulation

DSB-SC modulation implemented using Analog Devices ADC DAC 200 ksps on Virtex 2 FPGA.

Add comment February 21st, 2009

Microcontroller from Microchip

Just got this microchip microcontroller sdk today. It’s the 18 series. I can’t wait to start playing with it.

2 comments January 14th, 2009

ADC DAC Chipsets

I was testing on this ADC DAC chipsets at the Lab. Analog sent two each with next day delivery for free. Otherwise those can run to about 200 bucks. Kudos to Analog.

Add comment January 5th, 2009

The Famous Op-Amp

Operational Amplifier or so called ‘op-amp’ is the famous solid-state IC that uses external feedbacks to contorl its functions. It has a very high gain with one inverting input (V-), one non-inverting input (V+), one output (Vout), positive and negative power supply (Vs+ and Vs-). Most of the time we look at op-amp as an ideal op-amp to simplify things. In real life applications, op-amp behave almost like an ideal op-amp usually in MOSFET type op-amp. In ideal op-amp, it has an infinite open-loop gain, infinite bandwidth, infinite input impedance and zero output impedance.

This is a picture of op-amps including the famous 741. These small ICs are cheap in the cents per piece. The DC behavior of such real op-amp for its open-loop gain usually in the 100k to millions. The real op-amp does not have infinite gain and bandwidth. When the two inputs are equal in voltages, then the output is zero volt. The current entering the two inputs are small or can be assume to be zero.

Op-amp is usually use for filter design. A simple sallen-key low pass filter is shown done on SPICE. It tooks less than 10 minutes to actually build the circuit using the computer aided design software and simulation shows almost everything than can be done hands on in laboratory. Simulation is a good way to check your work in laboratory.

The plot shown is the frequency response of the filter output. As we could see, this is a pretty simple low-pass filter that allow signals to be passed below the 5 kHz range and reject anything above 10 kHz. There are many other different filter techniques that can be used in filter design according to the specifications. Op-amp is widely used in analog signal processing systems and in many other applications.

Add comment May 17th, 2006

Analog Designs

In analog designs, we deals with inputs and outputs that are continuous with values from the lowest potential Vss to the highest potential Vdd. There is so called the passive analog circuit which consumes no external power, and there is so called the active analog circuit which of course consumes external power to accomplish the designer’s task. The passive analog circuit involves the use of the basics devices such as resistors, capacitors, inductors and diodes. Whereas in active analog circuit involves the use of transistors and op-amps. Any of these circuits can be fabricated into analog IC chips. This brings us to the analog IC designs and also Mixed Analog and Digital VLSI circuits.

Add comment May 16th, 2006

Analog and Digital Designs

Analog is not old fashioned. I think analog is interesting and fun. If you are into electrical technical knowledge, then understanding analog design is a good point to start. In today’s world, analog and digital designs comes hand-in-hand. So to be good in both is a plus. I personally have the passion for the digital designs a lot more than the analog designs. One thing to know is that in real world, signals are in analog then digitized into today’s digital trends. The analog signals is known to be continuous and we could take these continuous signals and convert them into discrete digital signals. Digital design techniques are easier to design, data storage is much easier, much accurate, less noise and can be easily fabricated into Integrated Circuit chips. Analog design has always been a much involved process in compare to the digital design. In analog designs there are extra specifications to be taken care of such as the gain, bandwidth, signal distortion and noise. It tooks longer to master analog domain than the digital domain. More in-depth about analog designs which includes analog IC designs and can be easily simulated using Computer Aided Design software such as SPICE (Simulation Program with Integrated Circuit Emphasis). Also, more in-depth about digital designs which means TTL Gates (Transistor-Transistor Logic Gates), flip-flops, processor, CMOS, etc.

Add comment May 13th, 2006

Impedance Basics

So I was sitting around today wondering what I know about impedance. I come across the term impedance a lot in analog circuit design. If you understand ohm’s law and the concept of resistance in DC circuit, then impedance is the generalization of the concent from DC to AC. In short, impedance is basically a measure of the total opposition to the current flow in an AC circuit. It is made up of two components, the resistance and the reactance. Impedance (Z) is expressed in complex number. Z=R+jX. Where R is the resistance and X is the reactance.

In AC we not only have the amplitude, we also have the frequency and phase, therefore impedance not only allow the current to flow but also changes the phase, as frequency changes, it also changes the ampltitudes and phases. In ideal resistor, which means ignoring all the parasitics, we should expect to see the same impedance for all frequencies. In ideal cap, we will have the impedance that goes down with increasing frequency. In an inductor, we will have the impedance that goes up with increasing frequency.

There is a linear relation between impedances for capacitor and inductor with respect to frequency. The phase for inductor’s voltage is always 90 degrees ahead of its current. The capacitor’s current leads the voltage.

Simple MATLAB Script to calculate impedance is shown below.
Download impedance.m

% Matlab script to calculate impedance for series and parallel circuits
% Author: Ridwan Chendarma Chin
mode=input(’Select 1 for series and 2 for parallel: ‘);

C=input(’C= ‘);
R=input(’R= ‘);
L=input(’L= ‘);
f=input(’f= ‘);

X_C=1/(2*pi*f*C);
X_L=2*pi*f*L;

Z_C=(0-j*X_C);
Z_L=(0+j*X_L);
Z_R=(R+j*0);

if (mode == 2)
Z_T=1/((1/Z_C)+(1/Z_L)+(1/Z_R));
else
Z_T=Z_C+Z_L+Z_R;
end

Z_mag=abs(Z_T) % magnitude
Z_angle=angle(Z_T)*(180/pi) % angle in degrees

1 comment May 12th, 2006