Junction-transistor bootstrap linear-sweep circuits

Junction-transistor linear-sweep circuits of the `bootstrap¿ type are described for which deviations from perfect sweep linearity of much less than 1% are estimated to be possible. The operation of the circuits depends on the properties of the emitter-follower amplifier stage; these properties are shown to be very well suited for such applications. The basic bootstrap circuit is closely related to its thermionic-valve counter part and is very versatile, being readily arranged in externally gated, monostable or astable forms; a variety of useful waveforms such as rectangles or delayed pulses may be generated, in addition to the linear voltage sweep. One form of monostable circuit described is particularly precise in operation, the timing duration being defined by the comparison of an accurate linear voltage sweep waveform with a reference potential by means of a transistor blocking oscillator comparator. The limitations imposed on the circuits by the frequency-dependent properties of the transistors are investigated, and it is shown that these result in initial transients at the beginning of the sweep involving time-constants of the order 1/¿¿ furthermore, the transients concerned are not of a serious nature. Finally, quite fast, yet accurate, linear sweeps are shown to be possible, examples being given of circuits generating sweeps of less than 1 microsec duration.