Function generator
Encyclopedia
A function generator is a piece of electronic test equipment
or software used to generate different types of electrical waveform
s over a wide range of frequencies. These waveforms can be either repetitive or single-shot, in which case some kind of triggering source is required (internal or external). Usually 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.
One of the most useful features of the function generator is that it can be phase locked to an external signal source or another function generator. 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.
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. Some of the most common waveforms produced by the function generator are the sine, square, triangular and sawtooth waveforms.
from a cheese constant current source
. This produces a linear
ly 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 wave
s 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 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 they typically produce pure or modulated sine signals only.
Function generators, like most signal generator
s, may also contain an attenuator, 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
.
Some function generators can also generate white
or pink noise
.
More advanced function generators use Direct Digital Synthesis (DDS) to generate waveforms. Arbitrary waveform generator
s use DDS to generate any waveform that can be described by a table of amplitudes.
s. A function generator IC named ICL8038 (which is also used as Voltage Controlled Oscillator (VCO)) can be used to generate triangular wave, square wave, saw-tooth wave or even, sine wave simultaneously. For maximum voltage rating of 36, more than 300kHz of frequency can be generated.
generally, this means connecting the signal and ground leads to an oscilloscope to check the controls.
Adjust the function generator,to get the output signal correct, then attach the signal and ground leads
from the function generator to the input and ground of the device under test.
For some applications, the negative lead of the function generator should attach to a negative input of the
device, but usually attaching to ground is sufficient.A device such as an oscilloscope is then used to measure the circuit's output.
Electronic test equipment
Electronic test equipment is used to create signals and capture responses from electronic Devices Under Test . In this way, the proper operation of the DUT can be proven or faults in the device can be traced and repaired...
or software used to generate different types of electrical waveform
Waveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...
s over a wide range of frequencies. These waveforms can be either repetitive or single-shot, in which case some kind of triggering source is required (internal or external). Usually 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.
One of the most useful features of the function generator is that it can be phase locked to an external signal source or another function generator. 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.
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. Some of the most common waveforms produced by the function generator are the sine, square, triangular and sawtooth waveforms.
Working
A typical function generator usually comprises of a cheese 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. The triangular wave is generated by repeatedly charging and discharging a capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
from a cheese constant current source
Current source
A current source is an electrical or electronic device that delivers or absorbs electric current. A current source is the dual of a voltage source. The term constant-current sink is sometimes used for sources fed from a negative voltage supply...
. This produces a linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
ly ascending or descending voltage ramp. As the output voltage reaches upper and lower limits, the charging and discharging is reversed using a comparator
Comparator
In electronics, a comparator is a device that compares two voltages or currents and switches its output to indicate which is larger. They are commonly used in devices such as Analog-to-digital converters .- Input voltage range :...
, producing the linear triangle wave. By varying the current and the size of the capacitor, different frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
may be obtained. Sawtooth wave
Sawtooth wave
The sawtooth wave is a kind of non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw....
s 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
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....
square wave
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
is easily obtained by noting whether the capacitor is being charged or discharged, which is reflected in the current switching comparator 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
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
that can convert the triangle wave into a reasonably accurate sine wave
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...
. It does so by rounding off the hard corners of the triangle wave in a process similar to clipping
Clipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
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 they typically produce pure or modulated sine signals only.
Function generators, like most signal generator
Signal generator
Signal generators, also known variously as function generators, RF and microwave signal generators, pitch generators, arbitrary waveform generators, digital pattern generators or frequency generators are electronic devices that generate repeating or non-repeating electronic signals...
s, may also contain an attenuator, various means of modulating
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
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
Voltage-controlled oscillator
A voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage, while modulating signals may also be fed into the VCO to cause frequency modulation or phase...
) between two operator-determined limits. This capability makes it very easy to evaluate the frequency response
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
of a given electronic circuit
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
.
Some function generators can also generate white
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
or pink noise
Pink noise
Pink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
.
More advanced function generators use Direct Digital Synthesis (DDS) to generate waveforms. Arbitrary waveform generator
Arbitrary waveform generator
An arbitrary waveform generator is a piece of electronic test equipment used to generate electrical waveforms. These waveforms can be either repetitive or single-shot in which case some kind of triggering source is required...
s use DDS to generate any waveform that can be described by a table of amplitudes.
Features
The general features of a standard function generator are:- It can generate a wide range of frequencies ranging from 0.01 Hz to 100 kHz.
- It can be used to produce different waveforms like sine wave, square wave, triangular wave, sawtooth wave, etc.
- It offers great accuracy, about +/- 0.01% in the low frequency range.
- The distortion produced in the output signal is less than 1% 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 that 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.
Specifications
Some of the important specifications of function generator are given below:- Its specific frequency range is between 0.001Hz to 20MHz.
- Frequency stability of function generator is 0.05%.
- Distortion of function generator is -55dB below 50KHz and -40dB above 50KHz.
- Specific value of output amplitude(open circuit)is 10V(peak to peak).
- Specific value of output impedance is 50ohm.
- Different output waveforms like sine, square, triangular, ramp, pulse, AM and FM modulated, arbitary waves can be generated using the function generator.
Other meanings
Another type of function generator is a sub-system that provides an output proportional to some mathematical function of its input; for example, the output may be proportional to the square root of the input. Such devices are used in feedback control systems and in analog computerAnalog computer
An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...
s. A function generator IC named ICL8038 (which is also used as Voltage Controlled Oscillator (VCO)) can be used to generate triangular wave, square wave, saw-tooth wave or even, sine wave simultaneously. For maximum voltage rating of 36, more than 300kHz of frequency can be generated.
How to use a function generator
After powering on the function generator, the output signal needs to be configured to the desired shape.generally, this means connecting the signal and ground leads to an oscilloscope to check the controls.
Adjust the function generator,to get the output signal correct, then attach the signal and ground leads
from the function generator to the input and ground of the device under test.
For some applications, the negative lead of the function generator should attach to a negative input of the
device, but usually attaching to ground is sufficient.A device such as an oscilloscope is then used to measure the circuit's output.