Calibration of Waveform Generators

Calibration of Waveform Generators

A waveform generator is an electronic device that can generate a variety of electrical waveforms of a wide range of frequencies and amplitudes. The most common waveforms produced by the waveform generator which is also called signal generator are the sine wave, square wave or pulse, and sawtooth waves. These waveforms can be either cyclic or a single-shot which may be triggered from an internal or external source. The frequencies of these waveforms may be modified from a fraction of a hertz to hundreds of kHz.

The most important characteristic of a signal generator is its output frequency. Other properties such as accuracy of frequency, resolution of frequency, range of frequencies, and speed of switching, etc. are also quite relevant depending on the application. Other specifications that one should consider while selecting these generators are user interface, storage, memory, host connections, an interface bus, etc.

 

Applications of Waveform Generators

Waveform generators are very versatile devices as they are capable of producing a wide variety of waveforms and frequencies. Each waveform generated is specifically required for a particular application. Sinusoidal and square wave outputs are used in many diagnostic applications. The sawtooth and triangular wave outputs are used for those applications which require an increasing or decreasing signal at a specific linear rate. These include oscilloscopes and X-Y recorders.

Many waveform generators can simultaneously generate two different waveforms. This feature is required when two signals are required for a particular application. For example, a square wave may be generated for linearity measurements of an audio system, and in parallel a saw-tooth signal may be used with an oscilloscope, to provide the measurement result visually.

Some waveform generators have the capability of phase-locking their signal to an external signal source. One function generator may be used to phase lock a second waveform generator and the two output signals can be displaced in phase by an adjustable amount. Besides, one function generator may be phase-locked to a harmonic of the sine-wave of a second waveform generator.

Using two waveform generators, almost any waveform may be produced by the summation of the fundamental frequency generated by one waveform generator and the adjustable harmonics generated by another waveform generator.

The function generator can also be phase-locked to an accurate frequency standard, and all its output waveforms will have the same frequency, stability, and accuracy as the standard.

 

Types of Waveform Generators

Waveform Generators are classified into different types based on their functionality and applications. Following are some commonly used waveform generators:

  • Arbitrary Waveform Generators
  • RF Signal Generators
  • Audio Signal Generators
  • Video Signal Generator
  • Function Generator
  • Pulse Generator

 

Calibration of Waveform Generator

The accuracy of any electronic device suffers when it is used over time especially if it is used in harsh environmental conditions. Therefore routine calibration of these devices is an essential requirement. One of the most important considerations when calibrating signal sources is the highly accurate measurement of RF power traceable to calibration standards.

The calibration of a waveform generator usually also requires extensive measurements of analog modulation parameters such as AM, FM, and ϕM and their distortion such as signal-to-noise and distortion (SINAD) or total harmonic distortion (THD). In addition to the modulation parameters of the RF signal, the quality of the modulation signal (audio signal) has to be measured.

Most waveform generators provide output levels of +10 dBm to –130 dBm, which has to be measured accurately by the receiver. Power sensors can provide the most precise measurement results; however, their wide bandwidth limits their use to higher levels, above approx. –50 dBm. At lower levels, you have to use a frequency-selective measuring receiver whose absolute level error is corrected by a power meter. The measurement bandwidth and the noise figure of the receiver determine the lower measurement limit of the level measurement; the measurement error mainly depends on the display linearity of the receiver.

To calibrate signal generators, the frequency and level as well as the spectral purity of the output signal (phase noise, harmonics) must be determined. Accredited calibration labs follow diligent processes as they verify values and adjust instrumentation so that it operates according to specifications.

 

Calibration Interval

Regular calibration of your waveform generator is necessary so that it is ensured that its performance meets the manufacturer’s specifications. We recommend calibrating these instruments every year. You may choose the calibration interval according to your performance requirements but the calibration interval should never exceed two years.

 

Recommended Test Devices

The following devices are commonly used for calibration of waveform generators. These devices must have the same or better performance and specifications for calibration than the device under calibration.

  • Digital Multimeter
  • Digital Counter
  • Power Meter
  • Signal Generator
  • Frequency Counter
  • Spectrum Analyser
  • High-Frequency Oscilloscope
  • Power Sensor
  • 50 Ω Load
  • Cables and Adaptors

 

Wave Form Generator May Require Following Calibration Procedures:

  • Maximum Output Power
  • Power Level Accuracy
  • Internal Pulse Modulation Level Accuracy
  • Internal Pulse Modulation Rise/Fall Time
  • Internal Pulse Modulation Minimum Pulse Width
  • DC FM Carrier Offset
  • FM Frequency Accuracy
  • FM Distortion
  • Phase Modulation Distortion
  • Spurious Harmonics

e2b calibration provides reliable and cost-effective calibration services for all types of waveform generators. Our verifiable and traceable services are unmatched in the industry. We provide NIST traceable calibration and issue calibration certificates and calibration labels to meet your requirements. We are ISO-17025: 2017 compliant and registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. e2b calibration can also provide on-site calibration services.  Contact us for more information.

IN-HOUSE VS. OUTSOURCED CALIBRATION

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