RELATING TO SIGNAL PROCESSING

• US 20120027401A1
• Filed: 04/01/2010
• Published: 02/02/2012
• Est. Priority Date: 04/03/2009
• Status: Active Grant

• Current Assignee: BAE Systems Plc
• Original Assignee: BAE Systems Plc
• Inventors: Wood, John Michael, Pescod, Christopher Ralph
• Granted Patent: US 9,054,777 B2
• Time in Patent Office: Days
• US Class Current: 398/9
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes
• CPC Class Codes: H04B 10/2575 Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• CPC Class Codes: H04B 2210/006 Devices for generating or processing an RF signal by optical means

Abstract

A method of sampling a radio frequency signal comprises: receiving the radio frequency signal; modulating an optical signal with the radio frequency signal and an oscillator signal to generate a modulated signal; applying a filter to the modulated signal to generate an intermediate frequency signal, the filter having an intermediate pass band and an intermediate roll-off, the intermediate pass band and the intermediate roll-off in combination defining a intermediate frequency band having a first bandwidth; and sampling the intermediate frequency signal at a sampling frequency using a number of optically interleaved analogue-to-digital converters. The oscillator signal and the sampling frequency in combination are arranged such that the intermediate frequency band is defined between consecutive multiples of half of the sampling frequency.

Corresponding apparatus for sampling a radio frequency signal is also disclosed. Apparatus and methods for synthesising a radio frequency signal, using similar techniques to the above, are also disclosed.

Claims

1. A method of sampling a radio frequency signal comprising:

(i) receiving the radio frequency signal;

(ii) modulating an optical signal with the radio frequency signal and an oscillator signal to generate a modulated signal;

(iii) applying a filter to the modulated signal to select an intermediate frequency signal, the filter having an intermediate pass band and an intermediate roll-off, the intermediate pass band and the immediate roll-off in combination defining an intermediate frequency band having a first bandwidth; and

(iv) sampling the intermediate frequency signal at a sampling frequency using a number of optically interleaved analogue-to-digital converters;

the oscillator signal and the sampling frequency in combination being arranged such that the intermediate frequency band is defined between consecutive multiples of half of the sampling frequency.

2. A method as claimed in claim 1, wherein the frequency of the oscillator signal is variable such that the intermediate frequency band can be defined between consecutive multiples of half of the sampling frequency independently of the frequency of the radio-frequency signal.

3. A method as claimed in claim 2, wherein the frequency of the oscillator signal is tuneable.

4. A method as claimed in claim 2, wherein the frequency of the oscillator signal is switchable between a number of fixed frequency oscillator signals.

5. A method as claimed in claim 1, wherein the step of receiving of the radio frequency signal comprises:

applying a band-definition filter to the radio frequency signal, the band-definition filter having a band-definition pass band, and a band-definition roll-off, the band-definition pass band and the band definition roll-off in combination defining a second bandwidth generally equal to the first bandwidth.

6. A method as claimed in claim 5, wherein the band-definition pass band is switchable between a number of fixed-frequency bands.

7. A method as claimed in claim 1 wherein the intermediate frequency signal is defined between zero frequency and half of the sampling frequency.

8. A method as claimed in claim 1, wherein the sampling frequency is greater than 1 giga samples per second.

9. A method as claimed in claim 1, wherein the step of optically interleaving of a number of analogue to digital converters comprises:

(i) modulating an optical signal with the intermediate frequency signal to generate an optically-carried intermediate frequency signal;

(ii) passing the optically-carried intermediate frequency signal through an optical commutator switch, thereby generating a number of interleaved pulses;

(iv) detecting the interleaved pulses at a number of photodetectors, each of the photodetectors being associated with one of the analogue to digital converters.

27. A method as claimed in claim 1, wherein the sampling frequency is greater than 8 giga samples per second.

10. Sampling apparatus for sampling a radio frequency signal, the apparatus comprising:

(i) a receiver to receive a radio frequency signal;

(ii) a modulator to modulate an optical signal with the radio frequency signal and an oscillator signal to generate a modulated signal;

(iii) a filter operable to filter the modulated signal to select an intermediate frequency signal, the filter having an intermediate pass band and an intermediate roll-off, the intermediate pass band and the intermediate roll-off in combination defining an intermediate frequency band having a first bandwidth; and

(iv) a sampler to sample the intermediate frequency signal at a sampling frequency;

the oscillator signal and the sampling frequency in combination being arranged such that the intermediate frequency band is defined between consecutive multiples of half of the sampling frequency.

11. Apparatus as claimed in claim 10, wherein the frequency of the oscillator signal is variable such that the intermediate frequency band can be defined between consecutive multiples of half of the sampling frequency independently of the frequency of the radio-frequency signal.

12. Apparatus as claimed in claim 11, wherein the frequency of the oscillator signal is tuneable.

13. Apparatus as claimed in claim 12, wherein the frequency of the oscillator signal is switchable between a number of fixed frequency oscillator signals.

14. Apparatus as claimed in claim 10, wherein the receiver comprises:

a band-definition filter for filtering the radio frequency signal, the band-definition filter having a band-definition pass band, and a band-definition roll-off, the band-definition pass band and the band definition roll-off in combination defining a second bandwidth generally equal to the first bandwidth.

15. Apparatus as claimed in claim 14, wherein the band-definition pass band is switchable between a number of fixed-frequency bands.

16. Apparatus as claimed in claim 10 wherein the intermediate frequency signal is defined between zero frequency and half of the sampling frequency.

17. Apparatus as claimed in claim 10, wherein the sampling frequency is greater than 1 giga samples per second.

18. Apparatus as claimed in claim 10, wherein the number of optically interleaved analogue to digital converters comprise:

(i) a modulator to modulate an optical signal with the intermediate frequency signal to generate an optically-carried intermediate frequency signal;

(iii) an optical commutator switch operable to generate a number of interleaved pulses from the optically-carried intermediate frequency signal; and

(iv) a number of photodetectors to detect the interleaved pulses, each of the photodetectors being associated with one of the number of analogue to digital converters.

28. Apparatus as claimed in claim 10, wherein the sampling frequency is greater than 8 giga samples per second.

19. A method of synthesising a radio frequency signal comprising:

(i) generating an intermediate frequency signal from a digital signal using a number of optically interleaved digital to analogue converters;

(ii) generating a modulated signal by modulating an optical signal with the intermediate frequency signal and an oscillator signal; and

(iii) applying a first filter to the modulated signal to select the radio-frequency signal, the first filter having a first pass band and a first roll-off, and the first pass band and the first roll-off in combination defining a first bandwidth,

wherein an effective sample rate of the digital signal is selected such that the first bandwidth is less than, or equal to the bandwidth defined between consecutive multiples of half the effective sampling rate.

20. Synthesising apparatus for synthesising a radio frequency signal, the apparatus comprising:

(i) means to generate an intermediate frequency signal from a digital signal using a number of optically interleaved digital to analogue converters;

(ii) a modulator to modulate an optical signal with the intermediate frequency signal and an oscillator signal; and

(iii) a first filter operable to select the radio-frequency signal from the modulated signal, the first filter having a first pass band and a first roll-off, and the first pass band and the first roll-off in combination defining a first bandwidth,

wherein the effective sample rate of the digital signal is selected such that the first bandwidth is less than, or equal to the bandwidth defined between consecutive multiples of half the effective sampling rate.

21. Apparatus comprising:

a) a sampling apparatus for sampling a radio frequency signal, the sampling apparatus comprising;

(i) a receiver to receive the radio frequency signal;

(ii) a modulator to modulate an optical signal with the radio frequency signal and an oscillator signal to generate a modulated signal;

(iii) a filter operable to filter the modulated signal to select an intermediate frequency signal, the filter having an intermediate pass band and an intermediate roll-off, the intermediate pass band and the intermediate roll-off in combination defining an intermediate frequency band having a first bandwidth; and

(iv) a sampler to sample the intermediate frequency signal at a sampling frequency;

the oscillator signal and the sampling frequency in combination being arranged such that the intermediate frequency band is defined between consecutive multiples of half of the sampling frequency;

b) a synthesising apparatus for synthesising a radio frequency signal, the synthesising apparatus comprising;

(i) means to generate an intermediate frequency signal from a digital signal using a number of optically interleaved digital to analogue converters;

(ii) a modulator to modulate an optical signal with the intermediate frequency signal and an oscillator signal; and

(iii) a first filter operable to select the radio-frequency signal from the modulated signal, the first filter having a first pass band and a first roll-off, and the first pass band and the first roll-off in combination defining a first bandwidth,

wherein the effective sample rate of the digital signal is selected such that the first bandwidth is less than, or equal to the bandwidth defined between consecutive multiples of half the effective sampling rate; and

c) a digital radio frequency memory;

the sampling apparatus, synthesising apparatus and digital radio frequency memory being operable in combination to receive a radio frequency signal, digitally process the radio frequency signal, and to retransmit a processed radio frequency signal.

22. A method of sampling a radio frequency signal comprising:

(i) receiving the radio frequency signal;

(ii) modulating a signal with the radio frequency signal and an oscillator signal to generate a modulated signal;

(iii) applying a filter to the modulated signal to generate an intermediate frequency signal, the filter having an intermediate pass band and an intermediate roll-off, the intermediate pass band and the intermediate roll-off in combination defining an intermediate frequency band having a first bandwidth; and

(iv) sampling the intermediate frequency signal at a sampling frequency;

the oscillator signal and the sampling frequency in combination being arranged such that the intermediate frequency band is defined between consecutive multiples of half of the sampling frequency.

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