Simplified high frequency tuner and tuning method

• US 5,937,341 A
• Filed: 09/13/1996
• Issued: 08/10/1999
• Est. Priority Date: 09/13/1996
• Status: Expired due to Term

• Current Assignee: Washington Research Foundation (University of Washington)
• Original Assignee: University of Washington
• Inventors: Suominen, Edwin A.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Bhattacharya, Sam
• Application Number:
  US08/713,761
• Time in Patent Office: 1,061 Days
• Field of Search: 455/142, 455/143, 455/207, 455/302, 455/303, 455/305, 455/306, 455/316, 455/324, 455/338, 375/322, 375/324
• US Class Current: 455/324
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• 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 1/06 Receivers
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/16 Circuits
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178

Abstract

An RF tuner and tuning method employs analog quadrature mixing with a coarse-stepwise tunable local oscillator to a near-baseband passband region, followed by A/D conversion of the I and Q signals, correction of phase, group delay, and amplitude errors, image rejection, and translation to baseband by (1) fixed frequency translation, (2) stepwise channelized translation, or (3) essentially continuously variable tuning over a given digital tuning range. The near-baseband passband region is sized and located such that alternating image rejection provides non-redundant and complete tuning coverage of a desired high frequency spectrum with a local oscillator step size equal to about twice the digital tuning range or about twice the number of channels digitally stepwise tunable times the channel width, effectively doubling the typical local oscillator step size. The digital tuning is preferably performed by a continuously variable bandpass decimating filter with aliasing to within R_D of baseband, where R_D is the filter'"'"'s out put sampling rate, followed by fine-shifting to baseband by digital complex mixing. Demodulation is then accomplished according to signal type.

Image rejection and phase error and gain correction are preferably performed with a modified type III Hilbert transform pair with 90°±CF phase change and variable gain. The near-baseband passband is preferably centered at R/4 where R is the sampling rate entering the Hilbert transform.

Claims

1. A device for effecting frequency translation and selection of a signal of interest, said device comprising:

a. an analog portion including

i. a local oscillator for providing a first local oscillator signal having a frequency F_LO and a second local oscillator signal having the frequency F_LO approximately in quadrature to the first local oscillator signal,

ii. a first mixer for mixing the first local oscillator signal with an incoming signal providing thereby a first mixer output comprised of an upper high frequency signal spectrum of interest above F_LO and a lower high frequency spectrum of interest be low F_LO both translated to a near-baseband passband by mixing with the first local oscillator signal,

iii. a second mixer for mixing the second local oscillator signal with the incoming signal providing thereby a second mixer output comprised of the upper high frequency signal spectrum of interest above F_LO and the lower high frequency spectrum of interest below F_LO translated to the near-baseband passband by mixing with the second-local oscillator signal,

iv. a first filter for providing a first filter output by limiting the frequency spectrum of the first mixer output, and

v. a second filter for providing a second filter output by limiting the frequency spectrum of the second mixer output; and

b. a digital portion including

i. a first analog-to digital converter for providing a first converter output comprised of the first filter output converted from analog to digital format, and

ii. a second analog-to-digital converter for providing a second converter output comprised of the output of the second filter converted from analog to digital format;

wherein the digital portion is adapted and arranged to (1) correct phase errors and amplitude between the first converter output and the second converter output and combine the first and second converter outputs to provide an image-rejected signal within the near-baseband passband by substantially rejecting the near-baseband image of a selectable one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest, and (2) translate a selected portion of said near-baseband image-rejected signal to baseband, and wherein the local oscillator is a coarse-tunable local oscillator having a step size S and where the near-baseband passband extends from F₁ -F_A to F₂ +F_A and F₁ =k·

(F₂ -F₁) where F₁ is a first frequency, F₂ is a second frequency, k is a positive integer, and F_A is a given frequency adjustment, and where S=2·

(F2-F1), and wherein said first and second analog-to-digital converters sample the output of the first and second bandpass filters at a sampling rate R_A/D.

2. The device of claim 1 wherein the digital portion includes a type III Hilbert transform on one of the first and second converter outputs.

3. The device of claim 2 wherein the type III Hilbert transform is modified to produce a phase delay of 90 degrees plus a variable phase correction.

4. The device of claim 2 wherein the type III Hilbert transform receives samples at a sampling rate R and the near-baseband passband is centered at about R/4.

5. The device of claim 4 wherein R_A/D =R.

6. The device of claim 4 wherein R=R_A/D /M and wherein the first and second converter outputs are subjected to a first digital filtering and first decimation before the type III Hilbert transform, the first decimation being by a factor of M, the first digital filtering having stopbands at frequencies which would alias into the near-baseband passband at the sample rate R.

7. The device of claim 6 wherein the first digital filtering has stopbands only at frequencies which would alias into the near-baseband passband at the sample rate R.

8. The device of claim 4 wherein k=1.

9. The device of claim 1 adapted to receive a channelized signal spectrum having channel spacing of frequency C and wherein F₂ -F₁ =C·

N and N is the number of channels that fit simultaneously within the near-baseband passband, whereby every channel of the channelized signal spectrum is translatable to the near-baseband passband by a unique local oscillator frequency, and either of two different sets of N channels is selectably providable in the image-rejected signal for each local oscillator frequency by selectably rejecting the near-baseband image of one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest.

10. The device of claim 9 wherein F_A =(1/2)·

(W-C+W_ft) where W is the bandwidth of the channels to be received and W_ft is the width of any fine-tuning provided in the digital portion.

11. The device of claim 1 adapted to receive a channelized signal spectrum having channel spacing of frequency C and wherein F₂ -F₁ =C·

(N-1) and N is the number of channels that fit simultaneously within the near-baseband passband, whereby every channel of the channelized signal spectrum is translatable to the near-baseband passband by a local oscillator frequency, and either of two different sets of N channels is selectably providable in the image-rejected signal for each local oscillator frequency by selectably rejecting the near-baseband image of one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest.

12. The device of claim 11 wherein F_A =(1/2)·

(W+W_ft) where W is the bandwidth of the channels to be received and W_ft is the width of any fine-tuning provided in the digital portion.

13. The device of claim 1 wherein the desired portion of said near baseband image-rejected signal has a center frequency located within an essentially continuous tuning range of the digital portion of the device, said tuning range extending at least from F₁ to F₂ and wherein F_A equals one-half the bandwidth of the signals to be received.

14. The device of claim 13 wherein k=1.

15. The device of claim 1 wherein the desired portion of said near baseband image-rejected signal has a center frequency located within an essentially continuous tuning range of the digital portion of the device, said tuning range extending at least from F₁ to F₂ and wherein F_A equals one-half the bandwidth of the signals to be received plus a hysteresis amount F_H.

16. The device of claim 1 wherein an upper stopband of the first and second filters begins at a frequency F_usb such that F_usb ≦

R_A/D -(k+1)·

S/2-F_A.

17. The device of claim 16 wherein F_usb =R_A/D -(k+1)·

S/2-F_A.

40. The device of claim 1 wherein the digital portion is adapted and arranged to translate a selected portion of said near-baseband image-rejected signal to baseband by frequency translation.

18. A device for effecting frequency translation and selection of a signal of interest, said device comprising:

a. an analog portion including

i. a local oscillator for providing a first local oscillator signal having a frequency F_LO and a second local oscillator signal having the frequency F_LO approximately in quadrature to the first local oscillator signal,

ii. a first mixer for mixing the first local oscillator signal with an incoming signal providing thereby a first mixer output comprised of an upper high frequency signal spectrum of interest above F_LO and a lower high frequency spectrum of interest below F_LO both translated to a near-baseband passband by mixing with the first local oscillator signal,

iii. a second mixer for mixing the second local oscillator signal with the incoming signal providing thereby- a second mixer output comprised of the upper high frequency signal spectrum of interest above F_LO and the lower high frequency spectrum of interest below F_LO translated to the near-baseband passband by mixing with the second-local oscillator signal,

iv. a first filter for providing a first filter output by limiting the frequency spectrum of the first mixer output, and

v. a second filter for providing a second filter output by limiting the frequency spectrum of the second mixer output; and

b. a digital portion including

i. a first analog-to digital converter for providing a first converter output comprised of the first filter output converted from analog to digital format, and

ii. a second analog-to-digital converter for providing a second converter output comprised of the output of the second filter converted from analog to digital format;

wherein the digital portion is adapted and arranged to (1) correct phase errors and amplitude between the first converter output and the second converter output and combine the first and second converter output to provide an image-rejected signal within the near-baseband passband by substantially rejecting the near-baseband image of a selectable one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest, and (2) translate a selected portion of said near-baseband image-rejected signal to baseband, and wherein the digital portion includes a variable bandpass decimating filter for selecting the desired portion of said near-baseband image-rejected signal and translating the desired portion to within R_D /2 of baseband where R_D is the output sampling rate of the variable bandpass decimating filter.

19. The device of claim 18 wherein the incoming signal is an intermediate frequency signal produced by analog mixing.

20. The device of claim 18 adapted to transmit as well as receive a high frequency signal of interest.

21. A device for effecting frequency translation and selection of a signal of interest, said device comprising:

a. an analog portion including

i. a local oscillator for providing a first local oscillator signal having a frequency F_LO and a second local oscillator signal having the frequency F_LO approximately in quadrature to the first local oscillator signal,

ii. a first mixer for mixing the first local oscillator signal with an incoming signal providing thereby a first mixer output comprised of an upper high frequency signal spectrum of interest above F_LO and a lower high frequency spectrum of interest below F_LO both translated to a near-baseband passband by mixing with the first local oscillator signal,

iii. a second mixer for mixing the second local oscillator signal with the incoming signal providing thereby a second mixer output comprised of the upper high frequency signal spectrum of interest above F_LO and the lower high frequency spectrum of interest below F_LO translated to the near-baseband passband by mixing with the second local oscillator signal,

iv. a first filter for providing a first filter output by limiting the frequency spectrum of the first mixer output; and

v. a second filter for providing a second filter output by limiting the frequency spectrum of the second mixer output; and

b. a digital portion including

i. a first analog-to digital converter for providing a first converter output comprised of the first filter output converted from analog to digital format, and

ii. a second analog-to-digital converter for providing a second converter output comprised of the output of the second filter converted from analog to digital format;

wherein the digital portion is adapted and arranged to (1) correct phase errors and amplitude between the first converter output and the second converter output and combine the first and second converter outputs to provide an image-rejected signal within the near-baseband passband by substantially rejecting the near-baseband image of a selectable one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest, and (2) translate a selected portion of said near-baseband image-rejected signal to baseband, and wherein the digital portion includes a variable bandpass decimating filter for selecting the desired portion of said near-baseband image-rejected signal and translating the desired portion to within R_D /2 of baseband where R_D is the output sampling rate of the variable bandpass decimating filter, and wherein the digital portion further includes a complex multiplier for rotating to baseband the output of the variable bandpass decimating filter.

22. A device for effecting frequency translation and selection of a signal of interest having a maximum bandwidth W, said device comprising:

a. an analog portion including

i. a tunable local oscillator for providing a first local oscillator signal at a frequency F_LO and a second local oscillator signal at the frequency F_LO approximately in quadrature to the first local oscillator signal,

ii. a first mixer for mixing the first local oscillator signal with an incoming signal providing thereby a first mixer output comprised of an upper high frequency signal spectrum of interest above F_LO and a lower high frequency spectrum of interest below F_LO both translated to a near-baseband passband by mixing with the first local oscillator signal,

iii. a second mixer for mixing the second local oscillator signal with the incoming signal providing thereby a second mixer output comprised of the upper high frequency signal spectrum of interest above F_LO and the lower high frequency spectrum of interest below F_LO translated to the near-baseband passband by mixing with the second local oscillator signal,

iv. a first filter for providing a first filter output by limiting the frequency spectrum of the second mixer output; and

v. a second filter for providing a second filter output by limiting the frequency spectrum o the second mixer output; and

b. a digital portion including

i. a first analog-to-digital converter for providing a first converter output comprised of the first filter output converted from analog to digital format,

ii. a second analog-to-digital converter for providing a second converter output comprised of the second filter converted from analog to digital format,

iii. a variable phase delay type III Hilbert transform in a signal path following the first converter output,

iv. an allpass filter in a signal path following the second converter output having a nominal group delay equal to a group delay of the type III Hilbert transform,

v. an adder for combining the output of the type III Hilbert transform with the output of the all-pass filter to provide an image-rejected signal within the near-baseband passband by substantially rejecting the near-baseband image of a selected one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest, and

vi. a digital fine-tuning device having a near-baseband tuning range extending from a lower frequency F₁ to an upper frequency F₂ for selecting the desired signal of interest from within the image-rejected signal and translating said signal of interest to baseband;

wherein F₁ =k·

(F₂ -F₁) where k is a positive integer, and R=(F₁ +F₂), where R is the sampling rate of signals entering the type III Hilbert transform and the allpass filter, and wherein the near-baseband passband extends from about F₁ -W/2 to about F₂ +W/2, whereby only the middle of the Nyquist frequency range relative to R is employed as a passband during digital processing before and through the Hilbert transform.

23. The device of claim 22 wherein k=1.

24. The device of claim 22 wherein the first and second analog-to-digital converters are delta-sigma modulators each of which sample the respective output of first and second filters at a rate equal to M·

R, and wherein the delta-sigma modulators are each followed by a decimating filter with a decimation factor of M.

25. The device of claim 24 wherein the delta-sigma modulators are third-order.

26. The device of claim 22 wherein said selected portion comprises a portion of the frequency spectrum of the near-baseband passband and wherein correction of phase and amplitude errors is optimized for image rejection at frequencies corresponding to the selected portion.

27. A method of tuning radio frequency signal of interest comprising the steps of:

(a) subjecting the radio frequency signal to continuous-time quadrature mixing to produce I and Q signals in approximate quadrature relationship containing the signal of interest within a near-baseband passband;

(b) converting said I and Q signals to digital I and Q signals

(c) correcting errors between the digital I and Q signals and combining the digital I and Q signals so as to substantially reject an undesired mixing image,

wherein the continuous-time quadrature mixing is performed by mixing with a signal from a coarse-tunable local oscillator tunable in steps of size S, and wherein the near-baseband passband includes a frequency range extending from a lower frequency F₁ -F_A to an upper frequency F₂ +F_A, where F₁ is a first frequency, F₂ is a second frequency, and F_A is a given frequency adjustment, and wherein F1=k·

(F₂ -F₁) where k is a positive integer, and wherein S=2·

(F₂ -F₁).

28. The method of claim 27 wherein F_A =(1/2)·

(W-C+W_ft) where W is the bandwidth of channelized signals to be received from a channelized spectrum with channel spacing C, and where W_ft is the width of any fine-tuning performed in the step of selecting the signal of interest from the near-baseband passband and translating the signal of interest to baseband.

29. The method of claim 27 wherein F_A =W/2 wherein W is the maximum bandwidth of signals desired to be received.

30. The method of claim 27 wherein F_A =W/2+F_H wherein W is the maximum bandwidth of signals desired to be received and F_H is a hysteresis amount.

31. The method of claim 27 wherein the step of selecting the signal of interest from the near-baseband passband and translating the signal of interest to baseband comprises translating the signal of interest to baseband by frequency translation.

32. A method of tuning a radio frequency signal of interest comprising the steps of:

(a) subjecting the radio frequency signal to continuous-time quadrature mixing to produce I and Q signals in approximate quadrature relationship containing the signal of interest within a near-baseband passband;

(b) converting said I and Q signals to digital I and Q signals

(c) correcting errors between the digital I and Q signals and combining the digital I and Q signals so as to substantially reject an undesired mixing image,

wherein the step of combining the I and Q signals comprises;

subjecting one of said I and Q signals to filtration by a variable phase change type III Hilbert transform; and

subjecting the other signal to an allpass filter having the same nominal group delay as the variable phase change type III Hilbert transform.

33. The method of claim 32 wherein the near-baseband passband is centered at about R/4 where R is the sampling rate of signals entering the Hilbert transform and the allpass filter.

34. The method of claim 33 wherein R_A/D =R.

35. The method of claim 33 wherein the step of converting said I and Q signals to digital signals is performed by delta-sigma modulators, and where R=R_A/D /M, where M is the decimation ratio of a digital filtering and decimation process performed before the Hilbert transform and allpass filter and after the analog to digital conversion, the filtering portion of which process substantially rejects all frequencies not rejected by the continuous-time filtering step which would alias into the near-baseband passband at the sampling rate R.

36. The method of claim 32 further including the step of first subjecting a signal to continuous-time mixing to an intermediate frequency to produce a signal which is then subjected to the remaining steps of the method.

37. A method of tuning a radio frequency signal of interest comprising the steps of:

(a) subjecting the radio frequency signal to continuous-time quadrature mixing to produce I and Q signals in approximate quadrature relationship containing the signal of interest within a near-baseband passband;

(b) converting said I and Q signals to digital I and Q signals

(c) correcting errors between the digital I and Q signals and combining the digital I and Q signals so as to substantially reject an undesired mixing image,

wherein the step of translating the signal of interest to baseband is performed by a variable bandpass digital filtering and decimation process utilizing aliasing to alias the signal of interest to within R_D /2 of baseband where R_D is the sampling rate at the output of the variable bandpass digital filtering and decimation process, followed by digital quadrature mixing including multiplication by complex coefficients to rotate the signal of interest from within R_D /2 of baseband to baseband.

38. A device for effecting frequency translation and selection of a signal of interest, said device comprising:

a. an analog portion including

i. a local oscillator for providing a first local oscillator signal having a frequency F_LO and a second local oscillator signal having the frequency F_LO approximately in quadrature to the first local oscillator signal,

ii. a first mixer for mixing the first local oscillator signal with an incoming signal providing thereby a first mixer output comprised of an upper high frequency signal spectrum of interest above F_LO and a lower high frequency spectrum of interest be low F_LO both translated to a near-baseband passband by mixing with the first local oscillator signal,

iii. a second mixer for mixing the second local oscillator signal with the incoming signal providing thereby, a second mixer output comprised of the upper high frequency signal spectrum of interest above F_LO and the lower high frequency spectrum of interest below F_LO translated to the near-baseband passband by mixing with the second local oscillator signal,

iv. a first filter for providing a first filter output by limiting the frequency spectrum of the first mixer output, and

v. a second filter for providing a second filter output by limiting the frequency spectrum of the second mixer output; and

b. a digital portion including

i. a first analog-to digital converter for providing a first converter output comprised of the first filter output converted from analog to digital format, and

ii. a second analog-to-digital converter for providing a second converter output comprised of the output of the second filter converted from analog to digital format;

wherein the digital portion is adapted and arranged to (1) correct phase errors and amplitude between the first converter output and the second converter output and combine the first and second converter outputs to provide an image-rejected signal within the near-baseband passband by substantially rejecting the near-baseband image of a selectable one of the upper high frequency spectrum of interest and the lower high frequency spectrum of interest, and (2) translate a selected portion of said near-baseband image-rejected signal to baseband, and

wherein the digital portion includes a variable phase change type III Hilbert transform on one of the first and second converter outputs, and an allpass filter having the same nominal group delay as the variable phase change type III Hilbert transform on another of the first and second converter outputs.

39. The device of claim 38 wherein the type III Hilbert transform is modified to produce a phase delay of 90 degrees plus a variable phase correction.

41. A tuner comprising:

(a) a quadrature mixer responsive to an RF signal so as to produce therefrom in-phase and quadrature signals in approximate quadrature relation containing both a desired signal and an undesired mixing image,

(i) the desired signal being within a first one of (1) a positive frequency range and (2) a negative frequency range,

(ii) the undesired mixing image being within a second one of (1) the positive frequency range and (2) the negative frequency range, the second one being different from the first one; and

(b) a digital signal processing device coupled to the quadrature mixer so as to receive the in-phase and quadrature signals wherein the digital signal processing device is structured and arranged so as to both

(i) correct errors between the in-phase and quadrature signals and

(ii) combine the in-phase and quadrature signals so as to substantially reject the undesired mixing image,

wherein the digital signal processing device includes a variable bandpass decimating filter for selecting a desired portion of the combined in-phase and quadrature signals and translating the desired portion to within R_D /2 of baseband where R_D is the output sampling rate of the variable bandpass decimating filter.

42. The tuner of claim 41, wherein the digital signal processing device is structured and arranged to correct phrase errors between the in-phase and quadrature signals by changing the relative phase relationship between the in-phase and quadrature signals so as to place an undesired quadrature phasor into phase opposition with a corresponding in-phase phasor, regardless of the resulting phase relationship of a desired quadrature phasor the corresponding in-phase phasor, and wherein the digital signal processing device further includes a complex multiplier for rotating to baseband the output of the variable bandpass decimating filter.