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Browse Prior Art Database

MIXER SPURIOUS REDUCTION FOR INTEGRATED DETECTION RECEIVERS

IP.com Disclosure Number: IPCOM000009827D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-20
Document File: 3 page(s) / 155K

Publishing Venue

Motorola

Related People

Steven H. Arneson: AUTHOR

Abstract

Channelized receivers have many uses. They are used for determining the particular frequency band(s) in which signals are active or for separating the interference from various multiple signal emit~ ters closely spaced in frequency. Channelized search detection surveillance receivers and cellular base station receivers are two examples. The channeliza~ tion is typically performed in a filter bank located at a convenient center frequency for the filtering technology used. The center frequency input to this filter bank may not coincide to the absolute center frequency of the signals of interest and must be radio frequency, RF, translated for proper alignment.

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MOTOROLA

Technical Developments

MIXER SPURIOUS REDUCTION FOR INTEGRATED DETECTION RECEIVERS

by Steven H. Arneson

Channelized receivers have many uses. They are used for determining the particular frequency band(s) in which signals are active or for separating the interference from various multiple signal emit~ ters closely spaced in frequency. Channelized search detection surveillance receivers and cellular base station receivers are two examples. The channeliza~ tion is typically performed in a filter bank located at a convenient center frequency for the filtering technology used. The center frequency input to this filter bank may not coincide to the absolute center frequency of the signals of interest and must be radio frequency, RF, translated for proper alignment.

The necessary non-linear frequency translation process introduces spurious signal products that can limit the usable dynamic range of the receiver. A mixer with a local oscillator, LO, often provides the frequency translation. Its desired output is at the swn or difference frequency of the RF and LO frequency at the center frequency of the channelizer. Spurions signals also generated by this non-linear process at nLO x mRF frequencies, where m and n are positive or negative integers, interfere with and limit the dynamic range of operation throughout the channelized filter bank. When time sampling of signals or time integration of the signals is required, the methods of this paper can be used to extend the dynamic range of operation of the channelizer.

A channelized CW spectrum analysis receiver using digital fast Fourier transform, FFf, channelization that is frequency stepped across a larger input RF bandwidth serves as an example in describing the proposed invention. A representative block diagram is shown in Figure 1. Receivers using stepped or sweeping LO frequencies for RF frequency translation followed by some fonn of channelized frequency filtering with subsequent integration can improve their dynamic range relative to the nLO x mRF mixer spurs following the variable fre-

Motorola. Inc. 2000

quency LO by this proposed method of performing the integration and LO stepping process.

The advent of nwnerically controlled digital frequency synthesizer LO's, whose frequency can be switched almost instantaneously, make this method practical. Assume that on the first LO step the desired translated RF signal appears in the IF bandwidth at Bin 1 of the FFT output. The nLO x mRF spurs that occur in band for that frequency conversion scheme appear at the frequencies of several other FFT Bins at suppression levels defined by the mixer performance. For a single FFT computation, the dynamic range relative to these spurs is established by the ratio of the maximum signal level to the level of these spurious.

If we process and integrate many FFT computations at a fixed LO frequency, the signal to spur ratio will not change, and thus the dynamic range with respect to these spurs, would also r...