Logic Signal Sources

Types of Logic Signal Sources

• Pulse Pattern Generator (PPG)
• Data Timing Generator (DTG)

Logic sources are classified into pulse pattern generators and data timing generators. Pulse pattern generators drive a stream of square waves or pulses at very high frequencies from a small number of outputs. the high frequency and fast rise time capabilities of an advanced pulse generator make it an ideal tool to test high-speed digital equipment. The data timing generator generates volumes of binary information. The data timing generator is also called a pattern generator or data generator. It produces the streams of 1s and 0s needed to test computer buses, microprocessor IC devices, and other digital elements. The DTG can be used early in the product development cycle to substitute for system components that are not yet available.

Signal Generator Types

Signal Generators are broadly divided into the following:

• Analog and Mixed Signal Generators
  
  • Arbitrary Generators
    
    • Arbitrary/Function Generator (AFG)
    • Arbitrary Waveform Generator (AWG)

•  Logic Signal Sources (Pulse or pattern generators)

 Each of these types has unique strengths that may make it more or less suitable for specific applications. The arbitrary/function generator (AFG) offers fewer waveform variations than its AWG equivalent, but with excellent stability and fast response to frequency changes. Arbitrary generators answer almost any kind of signal generation needs. In the past, AFGs created their output signals using analog oscillators and signal conditioning. Now they use Direct Digital Synthesis (DDS) techniques to determine the rate at which samples are clocked out of their memory. The typical AFG has several standard waveforms stored in a preprogrammed part of its memory. In general, sine and square waves are the most widely used for many test applications.

Most AFGs offer some subset of the following familiar wave shapes:

• Sine
• Square
• Triangle
• Sweep
• Pulse
• Ramp
• Modulation
• Haversine

The arbitrary waveform generator (AWG) can produce any waveform you can imagine. Whether it is an RF signal to test a GSM or CDMA based telephone handset or a data stream for disk drive characterization. An arbitrary waveform generator (AWG) delivers waveforms based on stored digital data describing the constantly changing voltage levels of an AC signal. though the curve makes their spacing appear to vary. In an AWG, the sampled values are stored in binary form in a fast Random Access Memory (RAM). Some AWGs include separate digital outputs. These outputs fall into two categories: marker outputs and parallel data outputs.

Basic Waves

Following are the Basic types of waves:

1. Sine waves
2. Square and rectangular waves
3. Sawtooth and triangle waves
4. Step and pulse shapes
5. Complex waves

Sine waves are the most commonly known wave shape. Most AC power sources produce sine waves. The sine wave is the result of a basic mathematical function. Graphing a sine curve through 360 degrees will  produce a definitive sine wave image. The power switches at homes deliver power in the form of sine waves. In classrooms, while teaching about waves, teachers usually give examples of sine waves and use them for demonstration. Square and rectangular waves are at the heart of all digital electronics. A square wave is a voltage that switches between two fixed voltage levels at equal intervals, used for testing amplifiers. A rectangular wave has switching characteristics similar to those of a square wave, except that its high and low time intervals are not of equal length. Sawtooth and triangle waves look very much like the geometric shapes they are named for. The triangle wave has a symmetrical rise and fall times while the sawtooth ramps up slowly and evenly to a peak in each cycle, then falls off quickly.They are used to control other voltages in systems. A step wave shows a sudden change in voltage, as if a power switch had been turned on. The pulse is related to the rectangular wave.It is produced by switching up and then down, or down and then up, between two fixed voltage levels. A pulse may represent one bit of information traveling through a computer. A collection of pulses traveling together creates a pulse train. Complex waveforms may include elements of
sines, squares, steps, and pulses. In real life, waves rarely look like the examples in the graphics that we see here.