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Analogue, Time Drift Control for Sampling Oscilloscopes

IP.com Disclosure Number: IPCOM000084722D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Elliott, BJ: AUTHOR

Abstract

Because of difficult design problems associated with the time-base circuits of sampling oscilloscopes, the range of time position instability (drift) of a viewed wavefront is typically comparable to the system rise time. For the measurement and recording of very fast waveforms, this drift limits the accuracy because signal averaging methods (used to reduce the incoherent noise, and for recording) are not feasible.

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Analogue, Time Drift Control for Sampling Oscilloscopes

Because of difficult design problems associated with the time-base circuits of sampling oscilloscopes, the range of time position instability (drift) of a viewed wavefront is typically comparable to the system rise time. For the measurement and recording of very fast waveforms, this drift limits the accuracy because signal averaging methods (used to reduce the incoherent noise, and for recording) are not feasible.

Methods have been developed earlier that essentially eliminate time drift, for example, U.S. Patent 3,704,416, issued November 28, 1972 to B. J. Elliott et al and assigned to International Business Machines Corporation. However, the above methods use expensive and complex equipment, whereas for some applications a more conservative reduction factor may be adequate.

Described is a simple, inexpensive analogue technique that yields an improvement factor of about 50, which is adequate for many purposes. Negative feedback is applied to the DC bias level of the tunnel diode step-function generator, in order to stabilize the time position of the step wave front on the sampling oscilloscope (CRO).

In Fig. 1, a typical, viewed picosecond wavefront v(t) is shown. It represents the convolution of the step function generated by the tunnel diode with the impulse response of the 2-part network (under test) and the impulse response of the sampling CRO. After sampling, a repetitive, audio-frequency analogue signa...