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Circuit Providing Phase Shift Which is Variable with Frequency

IP.com Disclosure Number: IPCOM000091109D
Original Publication Date: 1969-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Rooney, JJ: AUTHOR

Abstract

A nonminimum phase shift network is provided in one transistor amplifier stage. Phase-shift variations of 180 degrees or 360 degrees occur as the frequency of the input varies from a selected lower limit to a selected upper limit. The class-A common emitter transistor amplifier 1 of drawing A includes emitter and collector resistors R4 and R3 and a negative feed-back circuit connected directly between the base-collector electrodes. The feedback circuit can comprise alternatively a capacitor C, an inductor L, a series LC circuit or a parallel LC circuit. If the feed-back comprises capacitor C, a phase shift from 180 degrees to 0 degrees occurs as frequency increases. If the inductor L is used, the phase varies from 0 degrees to -180 degrees.

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Circuit Providing Phase Shift Which is Variable with Frequency

A nonminimum phase shift network is provided in one transistor amplifier stage. Phase-shift variations of 180 degrees or 360 degrees occur as the frequency of the input varies from a selected lower limit to a selected upper limit. The class-A common emitter transistor amplifier 1 of drawing A includes emitter and collector resistors R4 and R3 and a negative feed-back circuit connected directly between the base-collector electrodes. The feedback circuit can comprise alternatively a capacitor C, an inductor L, a series LC circuit or a parallel LC circuit. If the feed-back comprises capacitor C, a phase shift from 180 degrees to 0 degrees occurs as frequency increases. If the inductor L is used, the phase varies from 0 degrees to -180 degrees. If either a series or parallel LC feedback is used, a phase shift from 180 degrees to -180 degrees or from 0 degrees to -360 degrees is achieved. The values of the resistors and the reactances are selected to provide a transfer function which achieves the variable phase shift as a function of input frequency. The preferred circuit uses resistors R3 and R4 of equal value so that the gate characteristic of the circuit is unity throughout the entire range of phase shift. Drawing B shows the gain and phase shift versus frequency characteristics of the circuit when the inductor L only is used and when R3 equals R4. Other feedback reactances provide different phase-shift...