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Browse Prior Art Database

IMPULSE FREQUENCY MULTIPLIER

IP.com Disclosure Number: IPCOM000007728D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-17
Document File: 4 page(s) / 183K

Publishing Venue

Motorola

Related People

Chris Brice: AUTHOR [+2]

Abstract

The invention provides a means ofachieving high multiples ofthe input frequency, while providing good efficiency at low cost. It is ideally suited to the VHF and UHF bands. Furthermore, since this circuit uses no transformers and basic components, it is rela- tively simple to integrate.

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MO7VROLA Technical Developments

IMPULSE FREQUENCY MULTIPLIER

by Chris Brice and Nigel Tolson

  The invention provides a means ofachieving high multiples ofthe input frequency, while providing good efficiency at low cost. It is ideally suited to the VHF and UHF bands. Furthermore, since this circuit uses no transformers and basic components, it is rela- tively simple to integrate.

UHF frequencies step recovery diodes become inef- ficient due to the very narrow "ON" time. At these frequencies, a much slower switch is required so that the null in the frequency spectrum appears much closer to the desired frequency, whereby a large amount of the energy appears in the lower order harmonics.

SUMMARY OF THE INVENTION

SOLUTION, DETAILED DESCRIPTION

PROBLEM

  It is quite common for radio systems to require signals that are direct multiples of some lower refer- ence frequency. Typical methods of implementing an integer Frequency multiplication are: transformer frequency doublers, non-linear tuned amplifiers, phase locked loops, step recovery diodes and varactor diodes. All of the above methods are either expen- sive and/or have high conversion loss. Furthermore, if the multiplied frequency is to be used in a hetero- dyne receiver or transmitter as a local oscillator, it must have a good phase noise profile. Indeed, the method used to produce this multiplied frequency must therefore contribute as little phase noise as possible (and hence have the minimum conversion loss).

  As will be appreciated, step recovery diodes can be utilized to provide frequency multiplication in the microwave band. In fact, a 10x multiplication factor (with good conversion gain) is readily achievable.

  Step recovery diodes used in frequency multipli- cation act as charge controlled switches. More par- ticularly, the diode changes from a high impedance state to a low impedance state for a very briefperiod (typically 100 picoseconds) with the resulting spec- trum extending well into the gigahertz region. Fur- thermore, up to the tirst null in the spectrum (as determined by the width ofthe switching impulse), the energy in the spectrum is shared fairly evenly between the harmonics. However, at VHF and low

  The present invention provides a very simple method of achieving good conversion gain of a ref- erence frequency, coupled with low cost and low complexity. Specifically, a switch having the desired characteristics can be realized using a simple differ- entiator and UHF transistor driven by a square wave (as shown in Figure 1). The time constant of the differentiator is set so that the null in the spectrum occurs aher the desired harmonic. A diode is used to remove the unwanted negative portion of the waveform, with the resulting positive portion then used to switch the transistor into conduction. A col- lector resistor is used to limit the current, while an output is taken from the collector of the transistor. The output is then bandpass filtered in either a lumped LC, cryst...