Introduction to FUNCTION GENERATOR

 Function generator:

Introduction:

It is a electronics instrument that used to produce different kinds of electrical waveform, over a wide range of frequencies.

 function generator waveforms may be either repetitive or single-shot, in which case some kind of triggering source is necessary (internal or external).

we can say that in other words ,A function generator produces waveform that is produced by the repetitive charging and discharging of the capacitor to which a constant energy source is connected. 

the most useful features of the function generator is that it can be phase locked to an external signal source or another function generator and Other important features of the function generator are continuous tuning over wide bands with max-min frequency ratios of 10 or more, wide range of frequencies from a few Hz to MHz, flat output amplitude and modulation capabilities like frequency sweeping, frequency modulation and amplitude modulation etc.

 The most common waveforms produced by the function generator are the sine, square, triangular and saw tooth waveforms etc...                                          

As we know that,Function Generators are used in testing of electronics circuits and  repair of electronic equipment,  to test amplifiers and development, , or to introduce an error signal into a control loop. 

Working :

following parts as,
1- frequency control network
2- upper constant current source
3-Lower constant current source
4-Integrator
5-compare-tor
6-resistance diode shaping circuit
7-Amplifier

 The triangular wave 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. 
 A function generator usually comprises of a triangular waveform whose frequency can be controlled smoothly as well as in steps.This triangular wave is used as the basis for all of its other outputs.

By varying the current and the size of the capacitor, different frequencies may be obtained. Saw tooth 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 saw tooth, i.e. slow rise and fast fall, or fast rise and slow fall.

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 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 output. using by a comparator other duty cycles (theoretically from 0% to 100%) can be obtained by it  and the saw tooth or triangle signal. 

A Function generators, like most signal generators, may also contain an attenuator and various means of modulating the output waveform, and often the ability to automatically and repetitively "sweep" the frequency of the output waveform (by means of a voltage-controlled oscillator) between two operator-determined limits. This capability makes it very easy to evaluate the frequency response of a given electronic circuit.

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

 features:

standard function generator have following  features as,
-It accuracy, about +/- 0.01% in the low frequency range.

-less than 1%,The distortion produced in the output signal is  for sine wave.  
-it can be phase locked to an external signal source or another function generator.
-it can be phase locked to a standard frequency, so  all the output waveforms of the generator will have the same accuracy and stability as that of the standard source.  
-It gives the availability of a continuous adjustable d.c. offset voltage between -5V to +5V.

That can be used to produce different waveforms like sine wave, square wave, triangular wave, saw-tooth wave, etc.

• It may generate a wide range of frequencies ranging from 0.01 Hz to 100 kHz.

How to use function generator?

After "on" the function generator, the output signal needs to be configured to the desired shape.  this means connecting ground leads and the signal leads  to an oscilloscope to check the controls.

Under test,To Adjust the function generator,and get the output signal correct, then attach the signal and ground leads from the function generator to the input and ground of the device .

For some kind of applications, the negative lead of the function generator should
 attach to a negative input of the device, but usually attaching to ground is sufficient.

such as an oscilloscope a device is  used to measure the circuit's output.