Direct conversion receiver with tri-phase architecture

• US 5,095,536 A
• Filed: 03/23/1990
• Issued: 03/10/1992
• Est. Priority Date: 03/23/1990
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Loper, Roger K.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Pham, Chi H.
• Application Number:
  US07/498,297
• Time in Patent Office: 718 Days
• Field of Search: 455/214, 455/245, 455/304-307, 455/313, 455/314, 455/324, 455/325, 455/337, 329/308, 329/309, 329/312, 329/313, 329/323, 329/327, 329/336, 375/77, 375/86, 375/102, 375/84, 375/85, 375/52, 375/83, 375/98
• US Class Current: 455/324
• CPC Class Codes: H03D 3/00 Demodulation of angle-, frequency- or phase- modulated oscillations H03D5/00, H03D9/00, H03D11/00 take precedence
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A direct conversion receiver having a tri-phase architecture including three separate baseband signal channels. RF communications signals which are being tuned by the receiver are split into three equal and in-phase components which are mixed with three equal but substantially out-of-phase injection signals on frequency with the communications signal. The resulting baseband component signals are independently filtered and amplified on the three signal channels. The baseband components are then directed to a signal processing unit which corrects the baseband components for gain or phase mismatch errors between the signal channels based on the information carried by the three components and thereafter demodulates the signals in order to acquire the information carried by the RF communications signal. An automatic gain control system and a signal filtering system adapted for use with direct conversion receivers are also disclosed.

Claims

1. A direct conversion radio receiver, comprising:

RF coupler means for splitting an RF communications signal into first, second and third RF components provided on separate first, second and third signal channels;

synthesizer and splitter means for generating an injection signal.on-frequency of said RF communications signal and splitting the same into first, second and third injection signal components which are out-of-phase with each other by approximately 120°

;

first, second and third mixer means installed on said first, second and third signal channels for mixing said first, second and third RF components with said first, second and third injection signal components in order to produce first, second and third baseband signal components;

first, second and third low-pass filter means installed on said first, second and third signal channels for filtering said baseband signal components from said first, second and third mixer means in order to reject interference and spurious signals accompanying said baseband components;

first, second and third amplification means installed on said first, second and third signal channels for amplifying said baseband signal components; and

signal processing means for processing the baseband components from said signal channels and using the information carried by these components to correct for gain or phase errors between the signal channels and demodulate these components so as to acquire the information carried by the RF communications signal.

2. The radio receiver of claim 1, further including:

RF amplification means for amplifying said RF communications signal prior to its supply to said RF coupler means.

3. The radio receiver of claim 1, further including:

RF filter means for pre-selecting the RF communications signal supplied to said RF coupler means.

4. The radio receiver of claim 1, wherein said first, second and third low-pass filter means each include a switched-capacitor filter.

5. The radio receiver of claim 1, further including:

automatic gain control means for controlling the gain of said first, second and third amplification means in order to regulate the amplitudes of said baseband signal components.

6. In a direct conversion receiver including a RF coupler for splitting a RF communication signal into RF components, first and second baseband signal channels having separate mixers, filters and amplifier units which are operative for processing said components, synthesizer means for generating an injection signal for supply to the mxiers associated with the signal channels and a signal processing unit for demodulating said communications signal based on its baseband components, the improvement comprising:

a third baseband signal channel having separate mixer, filter and amplifier units which are adapted for handling a signal component out-of-phase with the signal components on said first and second signal channels; and

signal processing means for correcting for phase or gain errors between said baseband signal channels based on the additional gain or phase information contributed by said third baseband signal channel.

7. The improvement of claim 6, further including:

means associated with said RF coupler for splitting said communications signal into three inphase and equal amplitude components; and

means associated with said synthesizer means for splitting said injection signal into three equal amplitude but out-of-phase components.

8. The improvement of claim 7, wherein said mean for correcting includes means for combining said components to form inphase and phase corrected quadrature elements.

9. The improvement of claim 7, wherein said signal processing unit includes three analog-to-digital converters separately acting on said first, second and third baseband signal components and a digital processing system operating under software control for correcting for phase or gain errors and acquiring the information carried by said communications signal from said baseband signal components.

10. The improvement of claim 6, wherein said filters in said baseband channels comprise switched-capacitor filters configured as low-pass filters.

11. The improvement of claim 6, further including:

automatic gain control means for regulating the amplitudes of the signal components on said baseband signal channels.

12. The improvement of claim 6, wherein said baseband signal channels include matched mixer, filter and amplifier units.

13. The improvement of claim 6, further including:

RF amplification means for amplifying said communications signal prior to its supply to said RF coupler; and

RF filter means for pre-selecting the communications signal supplied to said RF coupler.

14. A process for acquiring the information carried by an RF communications signal, comprising the steps of:

splitting said RF signal communications into three equal-amplitude and substantially in-phase RF components;

separately mixing said RF components with identical frequency equal-amplitude but substantially out-of-phase injection signals in order to form out-of-phase baseband components;

correcting for phase errors between said baseband components based on the phase information carried by three of said baseband components; and

demodulating said baseband components to acquire the information carried by the RF communications signals.

15. The process fo claim 14, further including the step of:

separately amplifying said baseband components to elevated power levels; and

separately low-pass filtering said baseband components to reject interference and spurious signals.

16. The process of claim 14, wherein said injection signals are produced by synthesizing a single injection signal, splitting the same into three equal-amplitude components and all-pass filtering these components to separately delay the phase of two of said components by approximately 120°

and 240°

.

17. The process of claim 14, further including the steps of:

pre-selecting and amplifying said RF communications signal prior to splitting the same into RF components.

18. A radio receiver characterized by a triangular architecture, said receiver comprising:

means for converting a RF communications signal into three out-of-phase baseband components;

means for separately filtering and amplifying each of said baseband components; and

means for correcting for phase or gain errors between said baseband components based on the phase or gain information carried by all three of said baseband components and demodulating said components to acquire the information carried by said RF communications signal.

19. The radio receiver of claim 18, wherein said means for converting includes means for splitting said RF communications signal into three equal-amplitude RF components, means for generating three identical frequency, equal-amplitude out-of-phase injection signals and means for separately mixing said RF components with said injection signals to form said baseband components.

20. The radio receiver of claim 18, wherein said means for separately filtering and amplifying includes three matched sets of analog filtering and amplifying units forming three separate channels for processing said baseband components.

21. The radio receiver of claim 18, wherein said means for correcting for phase or gain errors includes three analog-to-digital converters separately acting on said baseband components and a digital signal processing system operating under software control for correcting for phase or gain errors and acquiring the information carried by said RF communications signal from said baseband signal components.

22. The radio receiver of claim 18, further including:

RF amplification means for amplifying said RF communications signal prior to its supply to said means for converting.

23. A direct conversion receiver comprising:

means for splitting an RF communications signal into three RF components and converting these components into three out-of-phase baseband components;

three baseband signal channels adapted for separately amplifying and filtering said baseband signal components; and

signal processing means adapted for using the baseband signal components to correct for hardware induced phase errors between all three of said components.

24. The direct conversion receiver of claim 23, wherein said means for splitting and converting includes:

an RF coupler for splitting said RF signal into equal and inphase RF components,

means for generating three out-of-phase injection signals on frequency with said RF communications signal,

three mixers for separately mixing said RF components with said injection signals and thereby converting said RF components to baseband.

25. The direct conversion receiver of claim 23, wherein said signal processing means is also adapted for forming accurately phased apart inphase and quadrature baseband components and for demodulating said inphase and quadrature components.

26. The direct conversion receiver of claim 23, wherein said baseband signal channels are also adapted for digitizing said baseband signal components and said signal processing means comprises a digital signal processing module.

27. The direct conversion receiver of claim 23, wherein:

said baseband signal channels include one or more localized gain control loops containing only high-bandwidth components.

28. The direct conversion receiver of claim 27, wherein said components comprising said gain control loops include:

a plurality of gain control elements one of which is installed in each of said signal channels which are responsive to gain control signals,

means for generating a gain control signal correspondign to the voltage levels in short delay proximity to said gain control elements on said signal channels.

29. The direct conversion receiver of claim 23, further comprising:

a selectivity system adapted for controllable defining the audio bandwidth of the receiver suppressing off-channel signals, preserving the dynamic range of the receiver and maintaining the spectral purity of the baseband signals, said system including;

a plurality of matched low-pass active filters one of which is installed on each of said signal channels and which are cornered at a frequency somewhat greater than the audio bandwidth of the receiver so as to track each other closely over said bandwidth and yet suppress the greatest number of off-channel signals in order to help preserve the dynamic range of the receiver; and

a plurality of carefully matched low-pass quasi-digital or digital filters one of which is installed on each of said signal channels following said active filters and which are adjustable cornered so as to controllable define the audio bandwidth of the receiver and suppress all off-channel signals including any signals proximate to the audio bandwidth of the receiver.

30. The direct conversion receiver of claim 29, further comprising:

a plurality of matched low-pass LC filters cornered at a frequency very substantially greater than the audio bandwidth of the receiver so as to track each other closely over the audio bandwidth and suppress RF mixer products and large far off-channels signals.

31. The direct conversion receiver of claim 29, wherein said active filters are cornered at a frequency between 1.2-5 times the audio bandwidth of the receiver.

32. The direct conversion receiver of claim 30, wherein said LC filters are cornered at approximately 750 kHz, said active filters are cornered at approximately 33 kHz and said quasi-digital or digital filters are cornered at approximately 10 kHz.

33. The direct conversion receiver of claim 29, wherein said quasi-digital or digital filters are switched-capacitor filters.

34. The direct conversion receiver of claim 29, wherein said quasi-digital or digital filters are FIR digital filters.