INTRODUCTION:

An electronic instrument which generates periodic voltage or current waveforms that duplicate various types of well-defined mathematical functions. A signal generator, also known variously as function generator, pitch generator, arbitrary waveform generator, digital pattern generator or frequency generator. The simplest function generator usually generates a combination of square waves, triangular waves, and sine waves. It is used to generate electrical waveforms. They are generally used in designing, testing, troubleshooting, and repairing electronic or electro acoustic devices; though they often have artistic uses as well.

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Function Generators are used in development, testing and repair of electronic equipment, e.g. as a signal source to test amplifiers, or to introduce an error signal into a control loop

Function generators are typically used in simple electronics repair and design; where they are used to stimulate a circuit under test. A device such as an oscilloscope is then used to measure the circuit's output. Function generators vary in the number of outputs they feature, frequency range, frequency accuracy and stability, and several other parameters.

WORKING:Analog function generators usually generate a triangle waveform as the basis for all of its other outputs. The triangle is generated by repeatedly charging and discharging a capacitor from a constant current source. This produces a linearly ascending or descending voltage ramp. As the output voltage reaches upper and lower limits, the charging and discharging is reversed using a comparator, producing the linear triangle wave. By varying the current and the size of the capacitor, different frequencies may be obtained. Sawtooth waves can be produced by charging the capacitor slowly, using a current, but using a diode over the current source to discharge quickly - the polarity of the diode changes the polarity of the resulting sawtooth, i.e. slow rise and fast fall, or fast rise and slow fall.

A 50% duty cycle square wave is easily obtained by noting whether the capacitor is being charged or discharged, which is reflected in the current switching comparator's output. Other duty cycles (theoretically from 0% to 100%) can be obtained by using a comparator and the sawtooth or triangle signal. Most function generators also contain a non-linear diode shaping circuit that can convert the triangle wave into a reasonably accurate sine wave. It does so by rounding off the hard corners of the triangle wave in a process similar to clipping in audio systems.

A typical function generator can provide frequencies up to 20 MHz. RF generators for higher frequencies are not function generators in the strict sense since typically produce pure or modulated sine signals only.

CONTROLS : An AC signal generator or a function generator has various controls. With the help of a Snap chart, we will illustrate the controls of the function generator.

(1) Power switch: Turns the instrument on and off.

(2) Setting adjustment knob: Adjusts the parameter selected by the other buttons.

(3) Sine wave selection: Selects sine wave output.

(4) Counter/trigger input: Input terminal for frequency counting or external trigger signal. Note there is a maximum signal input rating.

(5) Ramp wave selection: Selects ramp (triangle) wave output.

(6) Modulation signal input: Input terminal for external modulation signal. Note there is a maximum signal input rating.

(7) Square wave selection: Selects square wave output.

(8) Synchronization signal output: Provides a signal (typically a square wave or pulse) that is in phase with the output signal; often at TTL levels.

(9) Amplitude-offset adjustment: Knob to adjust either the signal amplitude or DC offset voltage.

(10) Signal output: Output terminal for the function generator's signal. Usually has a 50 output impedance.

(11) Set to counter mode: Enables the counter input and displays the frequency of the input signal on item 4.

(12) Change utility settings: Adjust frequency sweep start frequency, sweep stop frequency, and display intensity.

(13) Set DC offset: Enable the adjustment of the DC voltage added to the signal output (control 10).

(14) Select modulation: Selects no modulation, internal AM modulation, external AM modulation, FM modulation deviation, and external FM modulation.

(15) Duty cycle: Adjusts the duty cycle or symmetry of the displayed waveform.

(16) Sweep: Turns the frequency sweep mode on and off and allows selection of a linear sweep or logarithmic sweep.

(17) Frequency: After pressing this button, the adjustment knob (control 2) will adjust the output signal's frequency.

(18) Mode: Selects the type of operation: continuous output, trigger repetition rate (sets the interval between the internal trigger; each trigger signal causes the generator to output one period), external trigger, manual trigger (pressing the → button causes one cycle to be output), or external gated (waveform cycles are output while the gate signal is above a threshold).

(19) Digit adjustment < : Moves the digit selection left.

(20) Digit adjustment > : Moves the digit selection right.

(21) Display: Shows the function generator's settings, such as frequency, amplitude, waveform selected, etc.

USES:A signal generator generates either audio or RF frequencies (depending on the capabilities and designed purpose of the generator) for testing other electronics equipment. Makes it easier to make tests on a device without having to have it "in circuit". It's a lot easier to test a piece of equipment on a work bench rather than trying to test it in place.

A function generator supplies TTL (transistor to transistor) square wave pulses, sine and sawtooth wave forms for various testing purposes. It's a lot easier to work on something on the work bench and being able to remove a circuit board and just supply power and a signal saves having to take a whole piece of equipment into the shop. Then again, you also can use an oscilloscope for troubleshooting when you have a good, known signal to work with. That applies to both types of generators.

CIRCUIT DIAGRAM: