Browse Prior Art Database

NOVEL, FREQUENCY CONVERTING QUADRATURE MODULATOR CIRCUIT

IP.com Disclosure Number: IPCOM000009566D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Sep-03
Document File: 2 page(s) / 104K

Publishing Venue

Motorola

Related People

Dan Tayloe: AUTHOR

Abstract

This quadrature modulator was invented as the inverse of a similar quadrature demodulator. This modulator design has the following advantages over normal quadrature modulation schemes: BASIC OPERATION This quadrature upconverter is essentially a sim- plified Tayloe quadrature product detector run back- wards. See Figure 1. Quadrature baseband inputs (0,90, 180, and 270 degrees) are switched on for a quarter cycle each in sequence at the desired RF fre- quency in a repeating cycle. The resulting RF signal needs only some filtering (lowpass or bandpass) to fuse the quadrature pieces back together at the new frequency.

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Developments Technical 0 M MO7WROl.A

 NOVEL, FREQUENCY CONVERTING QUADRATURE MODULATOR CIRCUIT

by Dan Tayloe

SUMMARY

  This quadrature modulator was invented as the inverse of a similar quadrature demodulator. This modulator design has the following advantages over normal quadrature modulation schemes:

l Less than 1 db of conversion loss

l No rf splitter required

  l Only one mixing element rather than the nor- mal two (one for I, one for Q).

  l Capable of direct RF up conversion of high level baseband signals (5-10~ pk-pk or more)

  l An extremely compact and simple design com- pared to other zero IF I-Q quadrature modulators.

  l The upconverter's upper frequency limit is set by the ability of a FET to be turned on for only a quarter cycle of the incoming RF being converted from baseband to rf. The maximum useful frequen- cy for this upconverter readily extends to at least 10 GHz.

Quadrature 4xF, Baseband In

Jl

BASIC OPERATION

  This quadrature upconverter is essentially a sim- plified Tayloe quadrature product detector run back- wards. See Figure 1. Quadrature baseband inputs (0,90, 180, and 270 degrees) are switched on for a quarter cycle each in sequence at the desired RF fre- quency in a repeating cycle. The resulting RF signal needs only some filtering (lowpass or bandpass) to fuse the quadrature pieces back together at the new frequency.

  FET rf transistors can be used as the switching elements in the above switch. Each of the four switching transistors conducts for only r/4 cycle its single baseband input to the RF output. Except for switch and filter losses, the upconversion process is essentially lossless.

  The quadrature upconverter requires as an input all four baseband phases. However, high speed inverting op-amps or simple differential drivers make it easy to create a 180 and 270 degree signals from the normal 0 degree "I" and 90 degree "Q" sig- nals, as show above in Figure 1.

COMMENTS

  The quadrature upconverter was built and test- ed. A "sort of superhet" was used to test this idea. A zero if product detector (Tayloe detector) was used to convert an incoming RF signal to a four phase quadrature baseband signal in order to pro- vide a four phase baseband signal source for the quadrature upcon...