The Kilomegacycle Sampling Oscilloscope

Oscilloscope Vintage
Fig. 2. Step response lypital of Model 187B ft!up-in. Sweep is 0.5 nsec/cm.
Oscilloscope Vintage
Fig. I. -hp- Model 185B Sampling Oscilloscope with dual-channel Model 187/Ï 1 kmc plug-in.

* I ' wO years ago the Hewlett-Packard laboratories developed a general-purpose oscilloscope which had the special property that its frequency response extended up to hundreds of megacycles. The oscilloscope was based on a technique called the sampling technique which enabled the instrument to have not only a very wide bandwidth but a high sensitivity as well. Since its introduction, this oscilloscope has come to be an indispensable tool for high-frequency and fast-circuit work. Its general convenience has brought to the nanosecond area oscilloscope techniques that were previously possible only in microsecond and slower circuits.

Over a period of time even the high performance of the original sampling oscilloscope has been advanced until the present instrument (Fig. 1 ) has a response extending to 1 kilomegacycle. The sensitivity of the instrument extends to 4 millivolts/cm, which at the other extreme can be attenuated to 200 mv/cm with a calibrated control. This range of sensitivities is combined with a vertical display thai is 10 cm high, thus giving the instrument the capability of handling large signals of 2 volts as well as small signals. A divider increases the large-signal capacity by 10 times when desired.

Besides the foregoing properties, the oscilloscope has a high impedance and one that exists at the probe input where it is available for practical use. The input resistance is 100 kilohms, while the input capacity is but 2 picofarads.

The oscilloscope has the additional convenience that the above characteristics are all incorporated in each channel of a dual-channel input, permitting simultaneous comparison of two fast phenomena. Further, these characteristics are determined by a vertical plug-in, giving the oscilloscope considerable additional flexibility, since another plugin is available to measure fast switching times (see p. 1),

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Although the sampling oscilloscope is mainly used with fast or high-frequency signals, it is not re stricted to such work, since its low-frequency response extends down to dc. Fast work, too, has its slower aspects in that it is often desirable in such work to be able to view all or a portion of a train of fast pulses or to view the slower signals that occur with some fast signals. To facilitate such usage, additional slow time scales have been incorporated into the oscilloscope. The slowest time scale at present is 10 microseconds

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