A signal generator is a device used to generate electronic signals with pre-defined properties of frequency, amplitude, and wave shape. These generated signals are used in designing and testing electronics devices including RF and Microwave systems.
Signal generators are available in different types for different purposes and applications. A few of the prime types are below.
A simple signal generator can be made using an oscillator with calibrated amplitude and frequency generation circuit. Modern signal generators will have the capability to generate different waveforms and have a microprocessor to control the signal generation.
To learn more about RF and Microwave, we recommend you to check the following Books.
To understand the signal generator operation in a better way, we recommend understanding the following components which are used along with the signal generators.
In this RF and Microwave signal generator article, we will cover,
Signal Generators are used for many of the RF and microwave test and high-end design applications, where a source signal is required. Below are a few of the specific applications of the signal generator.
The signal generator can be classified on the base of the waveform it can generate and on the base of the form factor of the unit. In addition, there are some special purpose signal generators are available in the Test and measurement domain
Signal generators are basically classified as function generators, arbitrary waveform generators, and RF and microwave signal generators on the basis of waveform generation and functionality.
A function generator is a device that generates repetitive waveforms like a sine wave, pulse or step waves, square waves, triangular waves, etc. A function generator contains an electronic oscillator or a digital signal processor with DAC to generate the required waveforms.
An arbitrary waveform generator will generate limited bandwidth frequency range, levels, and accuracy arbitrary waveforms. AWG allows the user to specify a variety of different waveform generation, hence it will be slightly expensive than a normal function generator.
RF (radio frequency) and microwave signal generators are used for the generation of RF signals in the range from a few kHz to 6 GHz and microwave signal generators are available in wide range frequency coverage, from few MHz to W bands. RF and microwave signal generators are mainly used for the test and measurement applications of RF components, subsystems, satellite and radar transceivers, cellular communications systems, etc.
Analog signal generators are classified into Radio-frequency and Audio-frequency signal generators. Even though both will use a sine-wave oscillator to generate the required signal, there will be a sharp distinction in design and purpose.
RF signal generators produce well-defined amplitude and frequency continuous wave RF signals as per the user requirements in the frequency range from few MHz to GHz. RF signal generators are capable of providing analog modulations like Amplitude modulation (AM), Frequency Modulation (FM), phase modulation(ΦM), and pulse modulation (PM). Based on the model and manufacturers, RF signal generators will be available with signal generation output powers ranging from -135 to +30 dBm.
Audio-frequency signal generators are used to generate accurate frequencies in the AF range and above. Audio-frequency signal generators are mainly used for checking the frequency response of audio equipment in electronic laboratories. AF signal generators also have the capability to vary the output power level as per the application requirements.
Vector signal generator, is also known as digital signal generator and it is used to generate digital-modulated RF signals like QAM, FSK, BPSK, QPSK, and OFDM. In addition, VSG will generate well-defined modern commercial industry-standard digital communication signals like GSM, CDMA2000, LTE, W-CDMA (UMTS), Wi-Fi (IEEE 802.11), WiMAX (IEEE 802.16), etc.
For example, for secure military communication systems that use transceivers with specific modulations, VSG allows the user to download the required modulation sequence into the vector signal generator and generate desired test signal for testing these transceivers.
A digital pattern generator or logic signal generator is used to produce logic signals that consist of 1 and 0 in the form of voltage levels with different analog characteristics such as rise time, fall time, high and low-level length, etc. Generally available standards for Digital pattern generators are LVTTL, LVCMOS.
A Video signal generator is used for the generation of these video graphics waveforms. It is primarily used for testing televisions and other video-based products like video games, online video transceivers, etc. These generators are capable of generating both composite and monochrome signals as per the test requirements. As nowadays due to digital processing, these generators are very rarely used.
RF signal generators are available in various form factors like benchtop, rackmount instruments, handheld, embeddable modules, and in USB and card-level formats.
Benchtop signal generators are AC power-operated instruments, mainly used in a lab environment of R&D, production, manufacturing area with good heat dissipation for the continued operation. Benchtop signal generators offer better modulation features in signal outputs.
These signal generators can be slotted into a 19 inch based test rack for the LAB testing requirements. Rack SG systems included PXI based signal generator with future expansion capabilities by adding the corresponding PXI card to the additional slots. This signal generator is ideal for the setting of an automated test setup.
Portable signal generators will have internal batteries for field test applications. These signal generators will have clearly viewable display for outdoor modulation settings and will be lightweight and have handles to carry around.
Handheld signal generators are very small in size and light-weighted instruments with limited capability of signal generation for field testing.
Networked signal generators will have web-browser access for the automated test requirements in the production and testing environment. These modules allow multi-source control and fast frequency switching. These units will have higher setting speeds and help to improve the time required for the completion of the test.
While choosing the signal generator for test and measurement applications it is important to check the following specifications to confirm the suitability of the instrument.
The frequency range of the signal generator indicates the lower and higher frequency it can generate. The frequency range will define as the range of frequency from start to stop.
The power output level of the generated RF signal from the signal generator is another factor that need to consider as various test required various level of signal power. In general signal, generators will generate signals with power in the range of -135dBc to +25dBc and have a variable attenuator to control the output power to the DUT.
The resolution of the signal generator specifies the minimal feasible frequency and amplitude increment of the source. A higher resolution is better for the application.
Need to choose an RF signal generator that is capable of generating all the required analog ( AM, FM, etc ) and digital modulations ( QAM, FSK, etc).
The accuracy of a signal generator indicates how close the source output frequency is with respect to the set frequency level.
Single Side Band phase noise indicates the amount of phase noise content in the generated RF signal from a signal generator. Lower the phase noise better the instrument.
Spurious and Harmonics are the signal generated at the multiples of the center frequency. Lower the Spurs and Harmonics components, better the signal generators.
The switching speed of the signal generator is calculated on the basis of how quickly the source varies from one frequency or amplitude level to another level. Higher the switching speed better the instrument.
External interface and RF connectors on the signal generators need to select as per the test setup requirements. For stand-alone units, it may not be a critical factor, but it is critical for the automated test requirements.
Signal generators is an instruments capable of providing complex and accurate frequency signals for RF test and measurement application. Signal generators are available as a dedicated instrument or come as a part of other instruments like radio communication analyzers, vector network analyzers, etc.
Below are the top signal generator manufacturers, who can offer a suitable instrument for your LAB signal source requirements.
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