Waveform Generators

              

A waveform generator is a device that produces repetitive waveforms at the desired frequency.  It can therefore generate sine, square, triangle, sawtooth, and other output waveforms. There are now many off-shelf waveform generator IC's that can be conveniently used and incorporated into a circuit that requires an auto-generated periodic waveform. Some examples of these waveform generator IC's are presented below, with brief descriptions provided by their respective manufacturers in their websites.

    

The ICL8038 waveform generator (manufactured by Intersil) is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.001Hz to more than 300kHz using either resistors or capacitors, and frequency modulation and sweeping can be accomplished with an external voltage.

    

The ICL8038 is fabricated with advanced monolithic technology, using Schottky barrier diodes and thin film resistors, and the output is stable over a wide range of temperature and supply variations. These devices may be interfaced with phase locked loop circuitry to reduce temperature drift to less than 250ppm/C. Key features include: Low Frequency Drift with Temperature 250ppm/C; Low Distortion 1% (SineWave Output); High Linearity 0.1% (Triangle Wave Output); Wide Frequency Range 0.001Hz to 300kHz; Variable Duty Cycle 2% to 98%; High Level Outputs TTL to 28V; Simultaneous Sine, Square, and Triangle Wave Outputs

  

The MAX038 (manufactured by Maxim) is a precision, high-frequency function generator that produces accurate sine, square, triangle, sawtooth, and pulse waveforms with a minimum of external components. The internal 2.5V reference (plus an external capacitor and potentiometer) lets the signal frequency be varied from 0.1Hz to 20MHz. An applied 2.3V control signal varies the duty cycle between 10% and 90%, enabling the generation of sawtooth waveforms and pulse-width modulation.

   

A second frequency-control input, used primarily as a VCO input in phase-locked-loop applications, provides 70% of fine control. This capability also enables the generation of frequency sweeps and frequency modulation. The frequency and duty-cycle controls have minimal interaction with each other. All output amplitudes are 2Vp-p, symmetrical about ground. The low-impedance output terminal delivers as much as 20mA, and a two-bit code applied to the TTL-compatible A0 and A1 inputs selects the sine, square, or triangle output waveform.

    

The XR8038A (manufactured by Exar) is a precision waveform generator IC capable of producing sine, square, triangular, sawtooth, and pulse waveforms, with a minimum number of external components and adjustments. The XR8038A allows the elimination of the external distortion adjusting resistor which greatly improves the temperature drift of distortion, as well as lowering external parts count. Its operating frequency can be selected over eight decades of frequency, from 0.001Hz to 200kHz, by the choice of external R-C components.

      

The frequency of oscillation is highly stable over a wide range of temperature and supply voltage changes. Both full frequency sweeping as well as smaller frequency variations (FM) can be accomplished with an external control voltage. Each of the three basic waveform outputs, (i.e., sine, triangle and square) are simultaneously available from independent output terminals. The XR8038A monolithic waveform generator uses advanced processing technology and Schottky barrier diodes to enhance its frequency performance.

    

References:   www.intersil.com;   www.maxim-ic.com;    www.exar.com

              

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