Signal Sources & Generators - Chapter 3

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Evolution of Function Generators during the 1960 to 1980 Period


A sample of the Hewlett Packard Function Generators produced
from 1952 up to the end of the 70s.
From bottom to top: HP 202A - HP 3300A - HP 3312A - HP 3311A




The Function Generator is another category of signal source on which these two decades of technology evolution would have a huge impact in terms of performance, accuracy and ease of use.

Starting with a 40 pounds vintage vacuum tube device, the HP 202A born in 1952, the first leap forward brought by transistor would leave place to the HP 3300A in 1965.

Further miniaturisation and components integration made possible a short time later the development of compact, lightweight and low-cost HP 3310A, HP 3311A, and HP 3312A, in 1970, 1973 and 1975 respectively.

Finally at the very end of the period, in 1979, adding the microprocessor technology to HP Lab developped Fractional N integrated circuits, HP introduced a state of the art, new generation of synthesized function generator with the HP 3325A.






1965, The HP 3300A Function Generator


The HP 3300A at work - From the Hewlett Packard Journal, November, 1965
Courtesy of Hewlett Packard Company


The HP 3300A Function Generator

The HP 3300A Function Generator
with Plug-in Versatility


The 3300A Function Generator was introduced in the 1965 catalog with its companion 3301A Auxiliary plug-in, 3302A Trigger / Phase Lock plug-in, and 3303A Divider plug-in.

The 3300A was designed in the HP Loveland laboratories with plug-in capability that enables it to be adapted for special applications. The basic instrument supplies sine, square, and triangular waves throughout a frequency range of 0,01 Hz to 100 kHz in seven decade ranges. With the HP 3302A Trigger / Phase Lock plug-in, the generator can also function as a tone-burst generator, as a low frequency pulse generator, as a frequency multiplier, and as a phase-locked oscillator with variable phase control. Additional flexibility of operation is made possible by the provision for electronic frequency control. The frequency may be controlled throughout any of the decade frequency ranges by an externally-supplied voltage applied through a rear-panel connector. The output frequency may thus be programmed, when used in automatic systems, or it may be swept or frequency-modulated by remote control.

Among other useful features, the instrument has two output stages supplying two separate waveforms for use in analog computers or other multiple waveform systems. Either output supplies any one of the three waveforms (sine, square, or triangular) independently of the other output and with amplitudes up to 35 volts peak-to-peak into an open circuit or 15 volts into 600 Ohms. Both outputs are short-circuit proof and may be terminated in any impedance with very little deterioration in the output signal (nominal output impedance is 600 ohms).
Each output is dc-coupled and has a separate, individually adjustable, 40 dB attenuator. In addition, one output may be switched to supply an inverted version of the waveform appearing at the other output, enabling the instrument to supply push-pull signals balanced to ground on any of the waveforms at any frequency. Loading of one output has no effect on the other.


Basic Circuitry of the Model HP 3300A - From the Hewlett Packard Journal, November, 1965
Courtesy of Hewlett Packard Company



HP 3310A Function Generator

The HP 3310A Function Generator


The HP 3310A was introduced in the 1970 catalog as a compact voltage-controlled function generator with 10 decades of range. Available output waveforms are sine, ramp, pulse, square and triangle plus DC offset and external voltage control.

The 3310A frequency range is from 0,0005 Hz to 5 MHz in 10 decade ranges with a 15 Volts peak to peak output into a 50 Ohms load and a plus or minus 5 Volts DC offset.

The 3310A introduction price was $575,00 USD in 1970.

A "B" version of the 3310 was introduced in the 1972 catalog. The 3310B has all the features and specifications of the standard 3310A plus single and multiple cycle output capability with either manual or external triggering.



Animation Display: Panoramic View of the HP 3310A Function Generator


The HP 3311A Function Generator

The HP 3311A,
Low Cost Function Generator

The HP 3311A is a typical example of the very few attempts made by HP to produce a low cost rather than a high performance instrument during the seventies.

Nevertheless, the HP 3311A offers wide functional capability at a modest price. Pushbutton range and function selection add convenience to versatility all over the seven decades of frequency from 0,1 Hz to 1 MHz.

The 10 V p-p output into 600 Ohms may be attenuated by >30 dB by a variable attenuator and offset by +/- 5 V on the three main functions which are: Sine, Square, and Triangle. A fourth function available is a separate pulse output suitable for synchronization or driving TTL logic circuits.




HP 3312A Function Generator

The HP 3312A
"Dual Function Generator"


The last improvement and most sophisticated Analog Function Generator produced by HP was introduced in the 1975 catalog and described in a 7 pages article in the March 1975 issue of the Hewlett Packard Journal.

The Model 3312A Function Generator combines two signal sources in a single box to produce a wide variety of test signals from 0,01 Hz to 13 MHz.

The two generators can be used separately for tests of multiple input devices such as modulators. On the other hand, the main generator can be amplitude or frequency modulated by the second generator (or an external source), giving the user a built-in choice of sine, square, or triangular waveform modulation.

The modulation generator can also gate or trigger the main generator to give single-cycle or multiple-cycle modes of operation. These modes greatly expand the variety of waveforms that the 3312A can produce. Narrow, low-duty-cycle pulse trains can be obtained by setting the main generator to a relatively high frequency and using the trigger mode with a low-frequency gating signal. Pulse bursts, useful for testing counting circuits, are obtained by using the multiple-cycle mode. The modulation generator can also sweep the main generator up to two decades in frequency at sweep rates as slow as 1 sweep per 100 seconds, useful for plotting frequency response on X-Y recorders, or at rates up to 100 sweeps per second for oscilloscope display.



The HP 3325A Synthesized Function Generator

The 3325A, Fractional-N
Synthesized Function Generator

Just before the end of the 70s, in 1979, the Fractional-N Synthesis technology permitted the production of the 3325A Synthesized Function Generator. The development of dedicated integrated circuits drasticaly reduced the quantity of discrete componants required to implement the Fractional-N synthesis technology in a variety of instruments.

The Model 3325A produces waveforms spanning 13 decades in frequency from 1 microHertz up to 21 MHz with synthesizer accuracy. Output waveforms can be sine waves, square waves, triangles and ramps with swept-frequency convenience. Output amplitude over the full frequency range is 1 mV to 10 V p-p into 50 Ohms. And like almost every new instrument at the end of the 70s, all necessary functions of the HP 3325A are HP-IB programmable.


HP 3325A simplified block-diagram - From the Hewlett Packard Journal, January, 1979
Courtesy of Hewlett Packard Company


Inside View of the HP 3325 Synthesized Function Generator (Zoomable)



Use your scrollwheel to zoom in/out
Click and drag to view other parts of the image when zoomed

Top-Inside View of the HP 3325A Synthesized Function Generator


Use your scrollwheel to zoom in/out
Click and drag to view other parts of the image when zoomed

Bottom-Inside View of the HP 3325B Synthesized Function Generator



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