Analog Fourier Transform Channelizer and OFDM Receiver

Abstract

An OFDM receiver having an analog multiplier based I-Q channelizing filter, samples and holds consecutive analog I-Q samples of an I-Q baseband, the I-Q basebands having OFDM sub-channels. A lattice of analog I-Q multipliers and analog I-Q summers concurrently receives the held analog I-Q samples, performs analog I-Q multiplications and analog I-Q additions to concurrently generate a plurality of analog I-Q output signals, representing an N-point discrete Fourier transform of the held analog samples, the I-Q signals having relative phase and magnitude representing bits in the OFDM sub-channels. The phase and magnitude may represent QPSK. Optionally, a phase shift decoder receives the analog transform I-Q output signals and generates a corresponding binary bit data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

FIG. 1 shows an example prior art digital FFT based OFDM receiver;

FIG. 2 is a functional block diagram showing one example OFDM receiver having one or more embodiments of the present invention;

FIG. 3 is an illustrative high-level circuit diagram of one example inventive analog multiplier based FFT circuit having one or more embodiments of the present invention;

FIG. 4 is an illustrative circuit diagram of one example of an inventive analog multiplier based butterfly circuit from FIG. 3;

FIG. 5 shows an example block flow diagram of one example simulation; and

FIG. 6 shows an example simulation result of one example QPSK constellation.

Claims

1. An analog multiplier based I-Q channelizing filter, comprising: a sample and hold circuit, constructed and arranged to receive an externally generated input signal, sample and hold N consecutive analog samples of the input signal N, and concurrently output the N consecutive analog samples as N held analog samples; andan analog-multiplier based Fourier Transform circuit, constructed and arranged to receive said N held analog samples and output a corresponding N analog transform signals representing an N-point discrete Fourier transform of said N held analog samples, wherein said Fourier Transform circuit includes a plurality of analog multipliers and analog summers.

2. The filter of claim 1, wherein said analog-multiplier based Fourier Transform circuit comprises a plurality of analog butterfly circuits, at least one of said analog butterfly circuits having R input terminal pairs and R output terminal pairs, an analog summer and an analog multiplier arranged between said R input terminal pairs and R output terminal pairs, and wherein said analog butterfly circuit is constructed and arranged to provide a steady-state transfer function representing a radix R butterfly between the R input terminal pairs and the R output terminal pairs.

3. The filter of claim 2, wherein R is equal to two, such that said butterfly circuit is constructed and arranged to provide a steady-state transfer function representing a radix-2 butterfly between two of said input terminal pairs and two of said output terminal pairs.

4. The filter of claim 1, wherein the sample and hold circuit is constructed and arranged to receive an externally generated input signal having an in-phase signal band and a quadrature signal band, and to sample and hold N consecutive analog samples of the input in-phase signal band and quadrature signal band signal N, and output said N consecutive analog samples as N sample pairs, each pair having an in-phase sample and a quadrature sample.

5. The filter of claim 4, wherein at least one of said analog multipliers includes a phase rotation circuit to receiving a signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an input I-Q magnitude and phase angle, and to output a phase rotated signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an output I-Q magnitude and phase angle related to said an input I-Q magnitude and phase angle by a predetermined phase rotation.

6. The filter of claim 2, wherein the sample and hold circuit is constructed and arranged to receive an externally generated input signal having an in-phase signal band and a quadrature signal band, and to sample and hold N consecutive analog samples of the input in-phase signal band and quadrature signal band signal N, and output said N consecutive analog samples as N sample pairs, each pair having an in-phase sample and a quadrature sample.

7. The filter of claim 6, wherein said analog multiplier includes a phase rotation circuit to receiving a signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an input I-Q magnitude and phase angle, and to output a phase rotated signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an output I-Q magnitude and phase angle related to said an input I-Q magnitude and phase angle by a predetermined phase rotation.

8. An OFDM receiver, comprising: an RF I-Q receiver constructed and arranged to receive an externally generated signal band, downconvert received externally generated signal band to an in-phase baseband signal and a quadrature baseband signal;an analog multiplier based I-Q channelizing filter, comprising: a sample and hold circuit, constructed and arranged to sample and hold N consecutive analog sample pairs, each sample pair being a sample of the in-phase baseband signal and a sample of the quadrature baseband signal, and concurrently output the N consecutive analog sample pairs as N held analog sample pairs, andan analog-multiplier based Fourier Transform circuit, having N inputs, N outputs, and a plurality of analog multipliers and analog summers connected between said N inputs and N outputs, constructed and arranged to receive said N held analog sample pairs on said N inputs, to and output on said N outputs a corresponding N analog transform signals, representing an N-point discrete Fourier transform of said N held analog samples, each of said N analog transform signals having an in-phase component signal and a quadrature component signal having respective magnitudes and polarities representing an I-Q phase and magnitude; anda phase shift decoder constructed and arranged to receive at least one of the N analog transform signals and to output a corresponding binary data, based on said I-Q phase and magnitude.

9. The OFDM receiver of claim 8, wherein said analog-multiplier based Fourier Transform circuit comprises a plurality of analog butterfly circuits, at least one of said analog butterfly circuits having R input terminal pairs and R output terminal pairs, an analog summer and an analog multiplier arranged between said R input terminal pairs and R output terminal pairs, and wherein said analog butterfly circuit is constructed and arranged to provide a steady-state transfer function representing a radix R butterfly between the R input terminal pairs and the R output terminal pairs.

10. The OFDM receiver of claim 9, wherein said analog-multiplier based Fourier Transform circuit comprises a plurality of analog butterfly circuits, at least one of said analog butterfly circuits having R input terminal pairs and R output terminal pairs, an analog summer and an analog multiplier arranged between said R input terminal pairs and R output terminal pairs, and wherein said analog butterfly circuit is constructed and arranged to provide a steady-state transfer function representing a radix R butterfly between the R input terminal pairs and the R output terminal pairs.

11. The OFDM receiver of claim 10, wherein R is equal to two, such that said butterfly circuit is constructed and arranged to provide a steady-state transfer function representing a radix-2 butterfly between two of said input terminal pairs and two of said output terminal pairs.

12. The OFDM receiver of claim 11, wherein at least one of said analog multipliers includes a phase rotation circuit to receiving a signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an input I-Q magnitude and phase angle, and to output a phase rotated signal having an in-phase component signal and a quadrature component signal, having respective magnitudes and polarities representing an output I-Q magnitude and phase angle related to said input I-Q magnitude and phase angle by a predetermined phase rotation.