CA2335960A1 - Simplified am stereo detector - Google Patents
Simplified am stereo detector Download PDFInfo
- Publication number
- CA2335960A1 CA2335960A1 CA002335960A CA2335960A CA2335960A1 CA 2335960 A1 CA2335960 A1 CA 2335960A1 CA 002335960 A CA002335960 A CA 002335960A CA 2335960 A CA2335960 A CA 2335960A CA 2335960 A1 CA2335960 A1 CA 2335960A1
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- Prior art keywords
- signal
- phase
- stereo
- signals
- quadrature
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-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04H—BROADCAST COMMUNICATION
- H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
- H04H20/44—Arrangements characterised by circuits or components specially adapted for broadcast
- H04H20/46—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95
- H04H20/47—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95 specially adapted for stereophonic broadcast systems
- H04H20/49—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95 specially adapted for stereophonic broadcast systems for AM stereophonic broadcast systems
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Stereo-Broadcasting Methods (AREA)
Abstract
Left and right stereo audio information is reproduced from a compatible quadrature amplitude modulation (C-QUAM) broadcast using a simplified approximation to true C-QUAM decoding. A synchronous detection approximation is used which avoids generating an envelope signal or calculating a cosine correction factor as in true C-QUAM
decoding. The method requires less intensive computation power thereby allowing a digital signal processor to perform other functions at the same time. The method produces no perceivable distortion or artifacts when reproducing normal broadcast material.
decoding. The method requires less intensive computation power thereby allowing a digital signal processor to perform other functions at the same time. The method produces no perceivable distortion or artifacts when reproducing normal broadcast material.
Description
.. .... .. .. .. ..
.. .. . .. . .. . ..
. . . . ... . ~ . . ... . . . .
.. . . ..
lr ~ 1 ~~ ~~~ ~~ ~~ 1~ .~
SIMPLIFIED AM STEREO DETECTOR
The present invention relates in general to a radio receiver for receiving compatible quadrature amplitude modulation (C-QUAM) stereo radio signals, and more specifically, to a simplified technique for detecting AM
stereo signals which requires less processing capacity while simultaneously improving signal quality for most typical broadcast signals and reception conditions.
1o In commercial AM or medium-wave broadcasting, stereo stations broadcast using compatible quadrature amplitude modulation (C-QUAM) signals so that non-stereo capable receivers can still receive a compatible monophonic signal.
As is known in the art, C-QUAM modulation involves phase modulating the stereo sum (L+R) and stereo difference (L-R) channels in quadrature followed by multiplying the phase components by a cosine correction factor. The signal is then limited to remove any amplitude variations and is finally amplitude modulated by the monophonic (L+R) signal.
At the receiver end, a non-stereo capable receiver receives a compatible signal by recovering just the final amplitude modulation. In a stereo receiver, phase information is recovered in order to detect the stereo channels. In a typical receiver, the in-phase (I) signal component and the quadrature-phase (Q) signal component are synchronously detected. An envelope detector detects the envelope of the received AM signal. The I signal and the envelope signal are compared in order to recreate the cosine correction factor. The I and Q signals are multiplied by the 3o correction factor to reverse the modulation process previously performed at the transmitter end. The cosine-corrected I and Q signals (or the envelope signal and the Q
signal) are input to a stereo decoder for decoding left and right stereo channels.
Receivers and decoders of this type are discussed in J. Lejeune: 'Stereo AM Radio Systems' an extract from TELEVISION Vol. 41, no.l of December 1990. This document AMENDED SHEET
.. .... .. .. .. ..
.. .. . .. ~ . .. . ..
_ . . . ... . . . ... . . . .
.. . . ..
.. ... .. .. .. ..
seeks to explain the various methods of modulating and decoding AM stereo signals, giving specific mention to Motorola's CQUAM system.
Many of the steps required in a typical C-QUAM receiver are computationally intensive which raises the cost of a receiver. For example, the envelope construction requires the calculation of a square root. In calculating the cosine correction factor, a divide calculation is required. In digital signal processing (DSP) hardware, these types of to calculations require a relatively greater amount of processing resources than other calculations such as multiplication and addition.
An audio output of a typical C-QUAM receiver can be extremely distorted during adverse signal reception conditions such as when over-modulation or co-channel interference exists. When these errors are introduced into the received signal, the ideal C-QUAM calculations suffer from exacerbated distortion due to phase errors.
In one aspect, the present invention provides a method 2o for reproducing left and right stereo audio signals in response to an AM stereo broadcast signal wherein a stereo sum signal and a stereo difference signal are modulated using compatible quadrature amplitude modulation including a correction factor, the method comprising the steps of:
~~~+~-. '~n.econverting the broadcast signal~~ Y+~~' to an intermediate frequency (IF) signal;
generating coherent sine and cosine injection signalsa=='=n===*.=~' in response to the IF
signal;
mixing the sine and cosine injection signals with the IF signal to produce an in-phase demodulated signal and a quadrature-phase demodulated signal, respectively; and coupling the in-phase and quadrature-phase demodulated signals to a AMENDED SHEET
' . . .. .... .. .. .. ..
.. .. . .. . .. . ..
_ . . . . .... .. .... .. ..
.. . : . . .. . . ..
_ . . : .. ... .. .. .. ..
stereo decoder matrix for decoding the left and right stereo audio signals ' without performing an envelope detection on the in-phase and quadrature- phase demodulated signals and without regenerating the correction factor.
In another aspect, the invention provides a radio receiver __, --~ ;-' ~'~~~~'~r.as hereinafter set forth in Claim 2 of the appended claims.
~,..- .. ..~ : +. ; .
The invention will now be described, by way of example, 2o with reference to the accompanying drawings, in which:
Figure 1 is a block diagram showing a prior art C-QUAM
receiver;
Figure 2 is a block diagram showing a simplified C-QUAM
stereo detector of the present invention; and Figure 3 is a flowchart showing a method embodied in the apparatus of Figure 2.
A typical implementation for a C-QUAM AM stereo receiver is shown in Figure 1. A broadcast signal is received via an antenna 10 and provided to a tuner 11 for producing an intermediate frequency (IF) signal at a standard intermediate frequency of 455 kHz, for example.
Depending upon the broadcaster, the IF signal may be modulated in C-QUAM format to provide stereo listening for C-QUAM receivers. A receiver may be implemented either in analog or digital form. For a digital implementation, an analogue-to-digital converter 12 digitizes a C-QUAM IF
AMENDED SHEET
.. .... .. .. .. ..
.: .. . .. . .. . ..
. . ... . . . ... . . . . .
.. . . ..
- . . .. ..-. .. .. .. ..
signal which is provided to an envelope detector 13. An envelope signal equal to 1+L+R is provided from envelope detector 13 to a DC blocking filter 14. After the DC offset is removed by DC blocking filter 14, an L+R signal is provided to a stereo decoder matrix 15 which produces right and left channel audio outputs.
The remainder of Figure 1 converts the C-QUAM IF signal to a regular QUAM IF signal in order to generate a difference signal L-R for input to matrix 15. Thus, the C-to QUAM IF signal is provided to a variable gain amplifier 16.
The output of amplifier 16 is coupled to an in-phase synchronous detector 17 and a quadrature-phase synchronous detector 20. The output of detector 17 provides an output signal corresponding to 1+L+R+ERROR to one input of a difference amplifier 18, where ERROR represents the cosine correction factor. The other input of difference amplifier 18 receives the 1+L+R signal from envelope detector 13.
Difference amplifier 18 is a high gain amplifier and provides an ERROR signal to the gain control input of 2o variable gain amplifier 16. The output of amplifier 16 is corrected for the ERROR and thus corresponds to a QUAM
signal.
The output of quadrature-phase synchronous detector 20 is connected to matrix 15 and to a phase detector 21. The QUAM signal from amplifier 16 is connected to another input of phase detector 21. The output of phase detector 21 is connected to a voltage controlled oscillator (VCO) 22 which provides a cosine signal to in-phase synchronous detector 17 and a sine signal (phase shifted by 90°s with respect to the 3o cosine signal) to quadrature-phase synchronous detector 20.
Thus, phase detector 21 and VCO 22 form a phase-locked loop.
The cosine and sine injection signals may also be generated using an adaptive line enhancer as is taught in U.S. Patent No. 5,357,574, .
In order to accurately reverse the modulation process performed at the transmitter, the receiver in Figure 1 performs envelope detection along with synchronous detection AMENDED SHEET
' . . .. .... .. .. .. ..
.-. .. . .. . .. . ..
. : . .... .. .... .. ..
.. . . ..
.. .:.. .. .. .. ..
in order to determine the cosine correction factor. When digital signal processing is used in Figure 1, the envelope detection requires performing a square root calculation and the correction factor calculation requires a division, which adds complexity to the DSP implementation. When the transmitted signal consists of a pure sinewave, these operations are essential in order to accurately decode the C-QUAM modulation with low distortion (e. g., less than about
.. .. . .. . .. . ..
. . . . ... . ~ . . ... . . . .
.. . . ..
lr ~ 1 ~~ ~~~ ~~ ~~ 1~ .~
SIMPLIFIED AM STEREO DETECTOR
The present invention relates in general to a radio receiver for receiving compatible quadrature amplitude modulation (C-QUAM) stereo radio signals, and more specifically, to a simplified technique for detecting AM
stereo signals which requires less processing capacity while simultaneously improving signal quality for most typical broadcast signals and reception conditions.
1o In commercial AM or medium-wave broadcasting, stereo stations broadcast using compatible quadrature amplitude modulation (C-QUAM) signals so that non-stereo capable receivers can still receive a compatible monophonic signal.
As is known in the art, C-QUAM modulation involves phase modulating the stereo sum (L+R) and stereo difference (L-R) channels in quadrature followed by multiplying the phase components by a cosine correction factor. The signal is then limited to remove any amplitude variations and is finally amplitude modulated by the monophonic (L+R) signal.
At the receiver end, a non-stereo capable receiver receives a compatible signal by recovering just the final amplitude modulation. In a stereo receiver, phase information is recovered in order to detect the stereo channels. In a typical receiver, the in-phase (I) signal component and the quadrature-phase (Q) signal component are synchronously detected. An envelope detector detects the envelope of the received AM signal. The I signal and the envelope signal are compared in order to recreate the cosine correction factor. The I and Q signals are multiplied by the 3o correction factor to reverse the modulation process previously performed at the transmitter end. The cosine-corrected I and Q signals (or the envelope signal and the Q
signal) are input to a stereo decoder for decoding left and right stereo channels.
Receivers and decoders of this type are discussed in J. Lejeune: 'Stereo AM Radio Systems' an extract from TELEVISION Vol. 41, no.l of December 1990. This document AMENDED SHEET
.. .... .. .. .. ..
.. .. . .. ~ . .. . ..
_ . . . ... . . . ... . . . .
.. . . ..
.. ... .. .. .. ..
seeks to explain the various methods of modulating and decoding AM stereo signals, giving specific mention to Motorola's CQUAM system.
Many of the steps required in a typical C-QUAM receiver are computationally intensive which raises the cost of a receiver. For example, the envelope construction requires the calculation of a square root. In calculating the cosine correction factor, a divide calculation is required. In digital signal processing (DSP) hardware, these types of to calculations require a relatively greater amount of processing resources than other calculations such as multiplication and addition.
An audio output of a typical C-QUAM receiver can be extremely distorted during adverse signal reception conditions such as when over-modulation or co-channel interference exists. When these errors are introduced into the received signal, the ideal C-QUAM calculations suffer from exacerbated distortion due to phase errors.
In one aspect, the present invention provides a method 2o for reproducing left and right stereo audio signals in response to an AM stereo broadcast signal wherein a stereo sum signal and a stereo difference signal are modulated using compatible quadrature amplitude modulation including a correction factor, the method comprising the steps of:
~~~+~-. '~n.econverting the broadcast signal~~ Y+~~' to an intermediate frequency (IF) signal;
generating coherent sine and cosine injection signalsa=='=n===*.=~' in response to the IF
signal;
mixing the sine and cosine injection signals with the IF signal to produce an in-phase demodulated signal and a quadrature-phase demodulated signal, respectively; and coupling the in-phase and quadrature-phase demodulated signals to a AMENDED SHEET
' . . .. .... .. .. .. ..
.. .. . .. . .. . ..
_ . . . . .... .. .... .. ..
.. . : . . .. . . ..
_ . . : .. ... .. .. .. ..
stereo decoder matrix for decoding the left and right stereo audio signals ' without performing an envelope detection on the in-phase and quadrature- phase demodulated signals and without regenerating the correction factor.
In another aspect, the invention provides a radio receiver __, --~ ;-' ~'~~~~'~r.as hereinafter set forth in Claim 2 of the appended claims.
~,..- .. ..~ : +. ; .
The invention will now be described, by way of example, 2o with reference to the accompanying drawings, in which:
Figure 1 is a block diagram showing a prior art C-QUAM
receiver;
Figure 2 is a block diagram showing a simplified C-QUAM
stereo detector of the present invention; and Figure 3 is a flowchart showing a method embodied in the apparatus of Figure 2.
A typical implementation for a C-QUAM AM stereo receiver is shown in Figure 1. A broadcast signal is received via an antenna 10 and provided to a tuner 11 for producing an intermediate frequency (IF) signal at a standard intermediate frequency of 455 kHz, for example.
Depending upon the broadcaster, the IF signal may be modulated in C-QUAM format to provide stereo listening for C-QUAM receivers. A receiver may be implemented either in analog or digital form. For a digital implementation, an analogue-to-digital converter 12 digitizes a C-QUAM IF
AMENDED SHEET
.. .... .. .. .. ..
.: .. . .. . .. . ..
. . ... . . . ... . . . . .
.. . . ..
- . . .. ..-. .. .. .. ..
signal which is provided to an envelope detector 13. An envelope signal equal to 1+L+R is provided from envelope detector 13 to a DC blocking filter 14. After the DC offset is removed by DC blocking filter 14, an L+R signal is provided to a stereo decoder matrix 15 which produces right and left channel audio outputs.
The remainder of Figure 1 converts the C-QUAM IF signal to a regular QUAM IF signal in order to generate a difference signal L-R for input to matrix 15. Thus, the C-to QUAM IF signal is provided to a variable gain amplifier 16.
The output of amplifier 16 is coupled to an in-phase synchronous detector 17 and a quadrature-phase synchronous detector 20. The output of detector 17 provides an output signal corresponding to 1+L+R+ERROR to one input of a difference amplifier 18, where ERROR represents the cosine correction factor. The other input of difference amplifier 18 receives the 1+L+R signal from envelope detector 13.
Difference amplifier 18 is a high gain amplifier and provides an ERROR signal to the gain control input of 2o variable gain amplifier 16. The output of amplifier 16 is corrected for the ERROR and thus corresponds to a QUAM
signal.
The output of quadrature-phase synchronous detector 20 is connected to matrix 15 and to a phase detector 21. The QUAM signal from amplifier 16 is connected to another input of phase detector 21. The output of phase detector 21 is connected to a voltage controlled oscillator (VCO) 22 which provides a cosine signal to in-phase synchronous detector 17 and a sine signal (phase shifted by 90°s with respect to the 3o cosine signal) to quadrature-phase synchronous detector 20.
Thus, phase detector 21 and VCO 22 form a phase-locked loop.
The cosine and sine injection signals may also be generated using an adaptive line enhancer as is taught in U.S. Patent No. 5,357,574, .
In order to accurately reverse the modulation process performed at the transmitter, the receiver in Figure 1 performs envelope detection along with synchronous detection AMENDED SHEET
' . . .. .... .. .. .. ..
.-. .. . .. . .. . ..
. : . .... .. .... .. ..
.. . . ..
.. .:.. .. .. .. ..
in order to determine the cosine correction factor. When digital signal processing is used in Figure 1, the envelope detection requires performing a square root calculation and the correction factor calculation requires a division, which adds complexity to the DSP implementation. When the transmitted signal consists of a pure sinewave, these operations are essential in order to accurately decode the C-QUAM modulation with low distortion (e. g., less than about
2~ THD). However, commercial broadcasts rarely include any to such pure sinewave as part of either a normal band-limited music or voice transmission. For the actual types of audio signals broadcast over commercial transmitters, an accurate reproduction of the audio is achieved by the present invention with far less computation by eliminating the envelope detection and calculation of the cosine correction factor, and instead using synchronous detection alone as an approximation.
When receiving under adverse reception conditions, such as during over-modulation or co-channel interference, phase 2o information is corrupted: In normal C-QUAM decoding, the calculation of the cosine correction factor is greatly impacted by the phase errors leading to large signal distortion in the detection. Under these conditions, the approximation of the present invention is less affected by the phase errors and so produces an audio output of better perceived quality to the listener.
Referring to Figure 2, a preferred embodiment of the present invention employs a coherent signal generator 25 receiving a C-QUAM IF signal from an A/D converter (not 3o shown). Generator 25 may be comprised of a phase-locked loop or an adaptive line enhancer as described above. A
_~Sine and cosine injection signals are provided to inputs of mixers 26 and 27, respectively. Mixers 26 and 27 also receive the C-QUAM IF signal. By mixing the sine and cosine injection signals with the IF signal, an in-phase demodulated (I) signal and a quadrature-phase demodulated (Q) signal are produced. In the present invention, the Q
AMENDED SHEET
.. .... .. .. .. ..
.~. .. . .. . .. . ..
. : . .:.. .. .... .. ..
.. . . ..
- v . .., w:~ .. .a signal from mixer 26 approximates the stereo difference signal L-R. However, the Q-signal from mixer 26 includes a 25 Hz stereo pilot signal which is removed by a pilot rejection filter 28. The approximated stereo difference signal is supplied to one input of a stereo decoder matrix 29. The I signal from mixer 27 provides an approximation of the envelope signal 1+L+R. The DC component is removed in a DC blocking filter 30 and the approximated stereo sum signal L+R is input to a second input of stereo decoder matrix 29.
to The sum and difference of the I and Q signal approximations is formed in matrix 29 by adders 31 and 32, respectively, thus producing the left and right audio signals.
In this preferred embodiment, the C-QUAM IF signal is generated at an intermediate frequency of zero Hz. Filters 28 and 30 may preferably be comprised of second order high pass filters.
The overall method of the present invention is shown in Figure 3. In step 35, a C-QUAM IF signal is generated. In step 36, coherent sine and cosine injection signals are 2o generated. In step 37, the injection signals are mixed with the IF signals to get the I and Q signals. Stereo is decoded from the I and Q signals in step 38 without using the C-QUAM cosine correction factor or performing envelope detection. Therefore, less computation is required in the DSP receiver and reception performance is improved during adverse signal conditions.
When receiving a C-QUAM encoded stereo broadcast, the I
signal of the present invention approximates the L=R
information plus a small error while the Q signal 3o approximates the L=-R information plus the same small error.
The small error introduces little perceivable distortion.
For a left only or right only stereo broadcast, the distortion introduced by this small error is equivalent to the distortion that would be present in a receiver using an ideal C-QUAM decoding.
When a broadcast consists primarily of stereo difference information (i.e., L=-R modulation), the error AMENDED SHEET
.~ w a. w v. v. ..
.. .. . . . . . . . . .
y y ..v . r . w. . . . . r . . . . . . . .
- . : t. ~~. . ~ wv ... ..
_ 7 _ introduced by the approximation can become quite large (approximately 20$ THD) especially at low frequencies (i.e., less than 300 Hz). However, this type of modulation is rarely involved at low frequencies due to limitations in normal recording techniques as well as phase cancellation which results in a playback for such signals. Thus, the approximation of the present invention may provide overall reception performance better than true C-QUAM detection under many reception rt -~~';~;~~~.conditions.
AMENDED SHEET
When receiving under adverse reception conditions, such as during over-modulation or co-channel interference, phase 2o information is corrupted: In normal C-QUAM decoding, the calculation of the cosine correction factor is greatly impacted by the phase errors leading to large signal distortion in the detection. Under these conditions, the approximation of the present invention is less affected by the phase errors and so produces an audio output of better perceived quality to the listener.
Referring to Figure 2, a preferred embodiment of the present invention employs a coherent signal generator 25 receiving a C-QUAM IF signal from an A/D converter (not 3o shown). Generator 25 may be comprised of a phase-locked loop or an adaptive line enhancer as described above. A
_~Sine and cosine injection signals are provided to inputs of mixers 26 and 27, respectively. Mixers 26 and 27 also receive the C-QUAM IF signal. By mixing the sine and cosine injection signals with the IF signal, an in-phase demodulated (I) signal and a quadrature-phase demodulated (Q) signal are produced. In the present invention, the Q
AMENDED SHEET
.. .... .. .. .. ..
.~. .. . .. . .. . ..
. : . .:.. .. .... .. ..
.. . . ..
- v . .., w:~ .. .a signal from mixer 26 approximates the stereo difference signal L-R. However, the Q-signal from mixer 26 includes a 25 Hz stereo pilot signal which is removed by a pilot rejection filter 28. The approximated stereo difference signal is supplied to one input of a stereo decoder matrix 29. The I signal from mixer 27 provides an approximation of the envelope signal 1+L+R. The DC component is removed in a DC blocking filter 30 and the approximated stereo sum signal L+R is input to a second input of stereo decoder matrix 29.
to The sum and difference of the I and Q signal approximations is formed in matrix 29 by adders 31 and 32, respectively, thus producing the left and right audio signals.
In this preferred embodiment, the C-QUAM IF signal is generated at an intermediate frequency of zero Hz. Filters 28 and 30 may preferably be comprised of second order high pass filters.
The overall method of the present invention is shown in Figure 3. In step 35, a C-QUAM IF signal is generated. In step 36, coherent sine and cosine injection signals are 2o generated. In step 37, the injection signals are mixed with the IF signals to get the I and Q signals. Stereo is decoded from the I and Q signals in step 38 without using the C-QUAM cosine correction factor or performing envelope detection. Therefore, less computation is required in the DSP receiver and reception performance is improved during adverse signal conditions.
When receiving a C-QUAM encoded stereo broadcast, the I
signal of the present invention approximates the L=R
information plus a small error while the Q signal 3o approximates the L=-R information plus the same small error.
The small error introduces little perceivable distortion.
For a left only or right only stereo broadcast, the distortion introduced by this small error is equivalent to the distortion that would be present in a receiver using an ideal C-QUAM decoding.
When a broadcast consists primarily of stereo difference information (i.e., L=-R modulation), the error AMENDED SHEET
.~ w a. w v. v. ..
.. .. . . . . . . . . .
y y ..v . r . w. . . . . r . . . . . . . .
- . : t. ~~. . ~ wv ... ..
_ 7 _ introduced by the approximation can become quite large (approximately 20$ THD) especially at low frequencies (i.e., less than 300 Hz). However, this type of modulation is rarely involved at low frequencies due to limitations in normal recording techniques as well as phase cancellation which results in a playback for such signals. Thus, the approximation of the present invention may provide overall reception performance better than true C-QUAM detection under many reception rt -~~';~;~~~.conditions.
AMENDED SHEET
Claims (6)
1. A method of reproducing left and right stereo audio signals in response to an AM stereo broadcast signal wherein a stereo sum signal and a stereo difference signal are modulated using compatible quadrature amplitude modulation including a correction factor, the method comprising the steps of:
converting the broadcast signal to an intermediate frequency (IF) signal;
generating coherent sine and cosine injection signals in response to the IF signal;
mixing the sine and cosine injection signals with the IF signal to produce an in-phase demodulated signal and a quadrature-phase demodulated signal, respectively; and coupling the in-phase and quadrature-phase demodulated signals to a stereo decoder matrix for decoding the left and right stereo audio signals without performing an envelope detection on the in-phase and quadrature-phase demodulated signals and without regenerating the correction factor.
converting the broadcast signal to an intermediate frequency (IF) signal;
generating coherent sine and cosine injection signals in response to the IF signal;
mixing the sine and cosine injection signals with the IF signal to produce an in-phase demodulated signal and a quadrature-phase demodulated signal, respectively; and coupling the in-phase and quadrature-phase demodulated signals to a stereo decoder matrix for decoding the left and right stereo audio signals without performing an envelope detection on the in-phase and quadrature-phase demodulated signals and without regenerating the correction factor.
2. A radio receiver for reproducing left and right stereo audio signals in response to an AM stereo broadcast signal wherein a stereo sum signal and a stereo difference signal are modulated using compatible quadrature amplitude modulation including a correction factor, the receiver comprising:
a tuner for converting the broadcast signal to an intermediate frequency (IF) signal;
a coherent signal generator (25) for generating coherent sine and cosine injection signals in response to the IF signal;
a first mixer (27) for mixing the IF signal with one of the injection signals to generate an in-phase (I) signal;
a second mixer (26) for mixing the IF signal with the other one of the injection signals to generate a quadrature-phase (Q) signal; and a decoder (29) for forming a sum and a difference of the I and Q signals without performing an envelope detection on the in-phase and quadrature-phase demodulated signals and without regenerating the correction factor.
a tuner for converting the broadcast signal to an intermediate frequency (IF) signal;
a coherent signal generator (25) for generating coherent sine and cosine injection signals in response to the IF signal;
a first mixer (27) for mixing the IF signal with one of the injection signals to generate an in-phase (I) signal;
a second mixer (26) for mixing the IF signal with the other one of the injection signals to generate a quadrature-phase (Q) signal; and a decoder (29) for forming a sum and a difference of the I and Q signals without performing an envelope detection on the in-phase and quadrature-phase demodulated signals and without regenerating the correction factor.
3. A radio receiver as claimed in claim 2, wherein the one injection signal is the cosine injection signal and the other one of the injection signals is the sine injection signal.
4. A radio receiver as claimed in claim 2 or 3, comprising a digital signal processor including the coherent signal generator (25), the first and second mixers (27,26), and the decoder (29).
5. A radio receiver as claimed in any of claims 2 to 4, wherein the coherent signal generator (25) is comprised of an adaptive notch filter.
6. A radio receiver as claimed in many of claims 2 to 4, wherein the coherent signal generator (25) is comprised of a phase-locked loop.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10460498A | 1998-06-24 | 1998-06-24 | |
| US09/104,604 | 1998-06-24 | ||
| PCT/GB1999/001975 WO1999067905A1 (en) | 1998-06-24 | 1999-06-23 | Simplified am stereo detector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2335960A1 true CA2335960A1 (en) | 1999-12-29 |
Family
ID=22301364
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002335960A Abandoned CA2335960A1 (en) | 1998-06-24 | 1999-06-23 | Simplified am stereo detector |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1090469A1 (en) |
| JP (1) | JP2002519889A (en) |
| CA (1) | CA2335960A1 (en) |
| WO (1) | WO1999067905A1 (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4236042A (en) * | 1979-03-12 | 1980-11-25 | Harris Corporation | Compatible AM stereo system employing a modified quadrature modulation scheme |
-
1999
- 1999-06-23 JP JP2000556463A patent/JP2002519889A/en active Pending
- 1999-06-23 WO PCT/GB1999/001975 patent/WO1999067905A1/en not_active Application Discontinuation
- 1999-06-23 CA CA002335960A patent/CA2335960A1/en not_active Abandoned
- 1999-06-23 EP EP99926659A patent/EP1090469A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP1090469A1 (en) | 2001-04-11 |
| JP2002519889A (en) | 2002-07-02 |
| WO1999067905A1 (en) | 1999-12-29 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |