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Measuring High-Frequency Transistor Characteristics

IP.com Disclosure Number: IPCOM000098208D
Original Publication Date: 1960-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 65K

Publishing Venue

IBM

Related People

Fekete, R: AUTHOR

Abstract

Heretofore a two channel heterodyne system such as that represented in the upper drawing has been employed to measure high frequency transistor parameters. Channels 10 and 11 are identical, each including in cascade a radio frequency amplifier 12, a mixer 13, and a frequency selective audio frequency amplifier 14. The output voltages of the amplifiers are measured by vacuum tube voltmeters 15 and 16 and the phase angle between the two by a phasemeter 17. A signal f(o) from a local oscillator is supplied by a terminal 18 to the mixers 13. The test device 19 represents the transistor under test and it has a suitable bias source 20.

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Measuring High-Frequency Transistor Characteristics

Heretofore a two channel heterodyne system such as that represented in the upper drawing has been employed to measure high frequency transistor parameters. Channels 10 and 11 are identical, each including in cascade a radio frequency amplifier 12, a mixer 13, and a frequency selective audio frequency amplifier 14. The output voltages of the amplifiers are measured by vacuum tube voltmeters 15 and 16 and the phase angle between the two by a phasemeter 17. A signal f(o) from a local oscillator is supplied by a terminal 18 to the mixers 13. The test device 19 represents the transistor under test and it has a suitable bias source 20. A radio frequency measuring signal f(r) of the required frequency and signal level is supplied by a terminal 21 to the input circuit of the transistor and to the input circuit of the radio frequency amplifier of channel 11. The output circuit of the transistor is connected to the input circuit of the radio frequency amplifier 12 of channel 10. Beat frequency signals f(a) in the audio frequency range, which are the heterodyne difference signals between the radio frequency signal f(r) and the local oscillator signal f(o), are developed in the output circuits of the mixers 13 and are selectively amplified in the amplifiers 14 to the exclusion of the other beat frequency components.

The determination of transistor parameters in the described system is reduced to the measurement of A.C. voltages and phase angles between them, or to the measurement of complex voltage ratios where the voltages are of the order of one millivolt. An advantage of the system resides in the fact that the actual measurement of the voltages takes place at an audio frequency where the necessary gain is easily provided by the frequency-selective amplifiers 14. However, the system is subject to a serious drawback. In the event of frequency instability of the measuring signal f(r) and the local oscillator signal f(o), the difference-frequency signal f(a) does not remain constant. Consequently an error in measurement results, or a complete disappearance of the signal f(a) occurs due to the narrow bandwidth of the tuned amplifiers 14. These shortcomings are avoided by the use with the system of additional apparatus.

In the center drawing a dual frequency generator 22 produces a first radio- frequency signal F((R)(1)) and second such signal F((R)(1)) + F(A). The latter has a frequency greater than the first signal by the audio-frequency signal F(A). Generator 22 is connected to frequency converters 23 and 24. A local oscillator 25 supplies a radio-frequency signa...