Determining the Amplitude Dependence of Negative Conductance in a Transistor Oscillator
Konttinen, Kristian (2016)
2016
Sähkötekniikan koulutusohjelma
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2016-06-08
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201605254077
https://urn.fi/URN:NBN:fi:tty-201605254077
Tiivistelmä
An electronic oscillator is an autonomous circuit that generates a periodic electronic signal. In practice, an oscillator should provide a voltage signal with a certain frequency and amplitude to a resistive load. Predicting the output voltage amplitude typically involves complicated nonlinear equations. One popular simplified approach to amplitude prediction uses the concept of negative output conductance. It assumes that the output conductance of the oscillator is a function of the output voltage amplitude. This function can then be used to predict the output voltage amplitude.
In literature, it is commonly assumed that the output voltage amplitude dependence of the negative conductance or resistance in a transistor oscillator can be approximated sufficiently accurately with a certain straight-line equation. Then a rule for maximizing the oscillator output power is derived based on this straight-line approximation. However, the straight-line equation has not been shown to be valid for transistor oscillators. Instead, the straight-line approximation was originally found to be suitable in describing the negative conductance of an IMPATT (IMPact Avalanche and Transit Time) diode. The validity of the rule for maximizing the output power is questionable for transistor oscillators.
This work studies the output voltage amplitude dependence of negative conductance in a transistor oscillator by simulations, measurements and analytical methods. Simulations are based on the harmonic balance technique. One simulation method determines the amplitude dependence by using a varying test voltage source, and the other method uses a varying load. The measurement method involves terminating the oscillator with a resistive load. The output voltage amplitude and the corresponding negative conductance are calculated from the measured output power for varying load conductance values. The analytical methods are based on a function describing the negative conductance of the transistor oscillator. This function is derived in this work. The results show that the straight-line based rule for maximizing the output power is inapplicable for transistor oscillators.
In literature, it is commonly assumed that the output voltage amplitude dependence of the negative conductance or resistance in a transistor oscillator can be approximated sufficiently accurately with a certain straight-line equation. Then a rule for maximizing the oscillator output power is derived based on this straight-line approximation. However, the straight-line equation has not been shown to be valid for transistor oscillators. Instead, the straight-line approximation was originally found to be suitable in describing the negative conductance of an IMPATT (IMPact Avalanche and Transit Time) diode. The validity of the rule for maximizing the output power is questionable for transistor oscillators.
This work studies the output voltage amplitude dependence of negative conductance in a transistor oscillator by simulations, measurements and analytical methods. Simulations are based on the harmonic balance technique. One simulation method determines the amplitude dependence by using a varying test voltage source, and the other method uses a varying load. The measurement method involves terminating the oscillator with a resistive load. The output voltage amplitude and the corresponding negative conductance are calculated from the measured output power for varying load conductance values. The analytical methods are based on a function describing the negative conductance of the transistor oscillator. This function is derived in this work. The results show that the straight-line based rule for maximizing the output power is inapplicable for transistor oscillators.