Fully integratable superheterodyne radio receiver utilizing tunable filters

• US 4,580,289 A
• Filed: 06/21/1984
• Issued: 04/01/1986
• Est. Priority Date: 12/30/1981
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Enderby, Ralph T.
• Primary Examiner(s): NG, JIN FAY
• Application Number:
  US06/625,350
• Time in Patent Office: 649 Days
• Field of Search: 455/22, 455/189, 455/197, 455/207, 455/209, 455/183, 455/260, 455/265, 455/266, 455/340, 455/314-316, 331/31, 331/38
• US Class Current: 455/314
• CPC Class Codes: H03D 7/161 all the frequency changers being connected in cascade

Abstract

A radio receiver from antenna to detector designed to be realized substantially on an integrated-circuit chip comprises a single tunable oscillator and a plurality of mixers. An input signal from an antenna is connected as an input to a first mixer and mixed with a signal derived from the oscillator. The signal may be taken directly, may be multiplied to a desired level or may be divided to a desired level. A particular output from the first mixer is selected by a first tunable filter. The output of the first tunable filter is taken as an input to a second mixer where it is mixed with a second signal derived from the oscillator. The process of mixing and application of the mixed signal to a tunable filter to select a desired frequency is continued as needed until the signal is reduced to a desired intermediate frequency range where it is amplified as needed to a level sufficient to drive a discriminator. Successive mixers receive, as inputs, signals that are derived by multiplication from the oscillator and that are in ratios to each other of integers of the order of two to eight. The center frequency of each of the tunable filters changes as different crystals or synthesized base frequencies are selected. This variation continues through the last intermediate frequency.

Claims

1. A method of converting a received radio signal at an antenna to an intermediate-frequency signal, the method comprising the steps of:

generating a first local-oscillator signal;

mixing the first local-oscillator signal with the received radio signal to produce a first sum of and difference between the first local-oscillator signal and the received radio signal;

deriving a first filter control signal from said first local oscillator signal for tuning a first automatically tunable filter to a center frequency approximately equal to one of said first sum of and difference between the first local oscillator signal and the received radio signal;

selecting one of the sum and the difference between the first local-oscillator signal and the received radio signal in said first automatically tunable filter;

dividing the first local-oscillator signal by an integer between two and eight to produce a second local-oscillator signal;

mixing the second local-oscillator signal with the selected one of the sum and the difference between the first local-oscillator signal and the received radio signal to produce a sum of and a difference between the second local-oscillator and the selected one of the sum and difference;

deriving a second filter control signal from said second local oscillator signal for tuning a second automatically tunable filter to a center frequency approximately equal to one of said first sum of and difference between the second local oscillator signal and the signal selected by said first automatically tunable filter; and

selecting one of the sum and the difference between the second local-oscillator signal and the selected one of the sum and difference between the first local-oscillator signal and the received radio signal in said second automatically tunable filter to produce an output signal, which output signal is the intermediate-frequency signal.

2. The method of claim 1 comprising in addition the steps of repeating the steps of dividing, mixing and selecting in a filter until a selected one of a sum and a difference is at a frequency that permits adequate adjacent channel selectivity.

3. The method of claim 2 wherein the frequency is less than 70 kilohertz.

4. The method of claim 2 comprising in addition the steps of:

dividing the first-control signal successively by each of a plurality of integers, each of said integers having a value between two and eight, to produce a successive control signal for each successive automatically tunable filter;

applying each successive control signal to each successive automatically tunable filter to control a frequency range of the successive automatically tunable filter.

5. A circuit for converting a received radio signal at an antenna to an intermediate frequency, the circuit comprising:

generating means for generating a first local-oscillator signal;

first mixing means connected to the antenna and to the means for generating a first local-oscillator signal to mix the first local-oscillator signal with the received radio signal to produce first sum and difference frequencies;

first automatically tunable selecting means connected to the first mixing means and responsive to said generating means for selecting one of the first sum and difference frequencies, said first selecting means having a center frequency set equal to said one of the first sum and difference frequencies exclusively by said generating means;

first means for dividing the frequency of the first local-oscillator signal by an integer between two and eight to produce a signal local-oscillator signal;

second mixing means connected to the first automatically tunable selecting means and to the first means for dividing, the second mixing means mixing the second local-oscillator and a selected one of the first sum and difference frequencies to produce second sum and difference frequencies; and

second automatically tunable selecting means connected to the second mixing means and responsive to said first dividing means for selecting one of the second sum and difference frequencies, said second selecting means having a center frequency set equal to said one of the second sum and difference frequencies exclusively by said first dividing means;

which selected one is the imtermediate frequency.

6. The circuit of claim 5 wherein the means for generating a first local-oscillator signal is tunable to select a desired broadcast channel.

7. The circuit of claim 5 comprising in addition:

second means for dividing the frequency of the second local-oscillator signal by an integer between two and eight to produce a third local-oscillator signal;

third mixing means connected to the second means for dividing and to the second selecting means, the third mixing means mixing the third local-oscillator signal and an output signal from the second selecting means to produce a third sum and difference frequecny; and

third automatically tunable selecting means connected to the third mixing means and responsive to said second dividing means for selecting one of the third sum and difference frequencies, said third selecting means having a center frequency set equal to said one of the third sum and difference frequencies by said second dividing means;

which selected one is an intermediate frequency.

8. The circuit of claim 7 comprising in addition:

third means for dividing the frequency of the third local-oscillator signal by an integer between two and eight to produce a fourth local-oscillator signal;

fourth mixing means connected to the third means and to the third selecting means, the fourth mixing means mixing the fourth local-oscillator signal and an output signal from the third selecting means to produce a fourth sum and difference frequency; and

forth automatically tunable selecting means connected to the fourth mixing means and responsive to said third dividing means for selecting on the fourth sum and difference frequencies, said fourth selecting means having a center frequency set equal to said one of the fourth sum and difference frequencies by said third dividing means;

fourth means for dividing the frequency of the fourth local-oscillator signal by an integer between two and eight to produce a fifth local-oscillator signal;

fifth mixing means connected to the fourth means for dividing and to the fourth selecting means, the fifth mixing means mixing the fifth oscillator signal and an output signal from the fourth selecting means to produce a fifth sum and difference frequency; and

fifth automatically tunable selecting means connected to the fifth mixing means and responsive to said fourth dividing means for selecting on of the fifth sum and difference frequency, said fifth selecting means having a center frequency set equal to said one of the fifth sum and difference frequencies by said fourth dividing means;

which selected one is an intermediate frequency.

9. A circuit for converting a received signal at an antenna to an intermediate frequency, the circuit comprising:

a local oscillator (16) producing a local-oscillator signal;

a multiplier (18) connected to the local-oscillator to produce a multiplied local-oscillator signal;

a first mixer (14) connected to the antenna and to the multiplier to produce a sum and a difference frequency between the received signal and the multiplied local-oscillator signal;

a first tunable filter (26) connected to the first mixer to select one of the sum and difference frequencies;

a second mixer (28) connected to the local-oscillator and to the first tunable filter to produce a sum and a difference frequency between an output signal from the first tunable filter and an output signal from the local-oscillator;

a second tunable filter (30) connected to the second mixer to select one of the sum and difference frequencies from the second mixer;

a first divider (34) connected to the local-oscillator to produce and output signal at a frequency equal to the frequency of the output signal from the local-oscillator divided by an integer between two and eight;

a third mixer (32) connected to the second tunable filter and to the first divider to produce a sum and a difference frequency between an output signal from the second tunable filter and an output signal from the first divider;

a third tunable filter (40) connected to the third mixer to select one of the sum and difference frequencies from the third mixer;

a second divider (36) connected to the first divider to produce an output signal at a frequency equal to the frequency of the output signal from the first divider, divided by an integer between two and eight;

a fourth mixer (38) connected to the third tunable filter and to the second divider to produce a sum and a difference frequency between an output signal from the second tunable filter and the output signal from the second divider;

a fourth tunable filter (42) connected to the fourth mixer to select one of the sum and difference frequencies from the fourth mixer;

a third divider (46) connected to the second divider to produce an output signal at a frequency equal to the frequency of the output signal from the second divider, divided by an integer between two and eight;

a fifth mixer (44) connected to the fourth tunable filter and to the third divider to produce a sum and a difference frequency between an output from the fourth tunable filter and the output signal from the third divider;

a fifth tunable filter (48) connected to the fifth mixer to select one of the sum and difference frequencies from the fifth mixer;

a fourth divider connected to the third divider and to the fifth tunable filter to produce a signal at a frequency equal to the frequency of the third divider, divided by an integer between two and eight, and to control a center frequency of the fifth tunable signal at the frequency of the signal produced by the fourth divider; and

means connected to the first, second, third, fourth and fifth tunable filters for tuning the center frequencies of the filters as an exclusive function of frequency of the local-oscillator signal.

10. The circuit of claim 9 wherein the local-oscillator (16) comprises a tunable local oscillator (16, 20, 22, 24).

11. The circuit of claim 9 wherein the center frequency of the fifth tunable signal is less than 70 kilohertz.

12. A circuit for converting an input signal to an intermediate frequency, comprising:

frequency generator means for generating signals at any of a plurality of integer related frequencies;

a mixer for receiving said input signal and mixing said input signal with a first one of said generated signals to produce said intermediate frequency signal; and

a tunable filter, having an external frequency input responsive to a second one of said generated signals to control the center frequency of said tunable filter, said external frequency input being coupled to said frequency generator means, said tunable filter coupled to said mixer for passing said intermediate frequency signal while attenuating undesired frequencies, whereby the center frequency of said tunable filter is exclusively determined by said frequency generating means and is set equal to said intermediate frequency.

13. The circuit of claim 12, further including:

a second mixer for receiving said intermediate frequency and mixing said intermediate frequency with a third one of said generated frequencies to produce a second intermediate frequency; and

a second tunable filter having an external frequency input responsive to a fourth one of said generated signals to control the center frequency of said second tunable filter, said external frequency input being coupled to said frequency generator means, said second tunable filter coupled to said second mixer for passing said second intermediate frequency while attenuating undesired frequencies, whereby the center frequency of said second tunable filter is exclusively determined by said frequency generating means and is set equal to said second intermediate frequency.

14. The circuit of claim 13, wherein said frequency generator means includes a frequency synthesizer.

15. A circuit for converting an input signal to an intermediate frequency, comprising:

frequency sythesizer means for generating signals at any of a plurality of generated frequencies, said frequency synthesizer means including a reference frequency generator for producing a preferenced frequency, a VCO for producing a VCO frequency and a phase comparator having an error signal output, said error signal output providing an error signal relating the phase of the reference frequency with the phase of the VCO frequency;

a mixer for receiving an input signal and mixing said input signal with one of said plurality of generated frequencies to produce an intermediate frequency signal; and

a tunable filter, operatively coupled to said error signal output of said phase comparator and responsive thereto so that the center frequency of said tunable filter is determined exclusively by said phase comparator error signal output and set equal to said intermediate frequency, said tunable filter coupled to said mixer for passing said intermediate frequency signal while attenuating undesired frequencies;

whereby, said tunable filter automatically adjusts to changes in said generated frequencies so that proper filtering of said intermediate frequency signal is maintained.

16. A superheterodyne receiver system capable of receiving signals on a plurality of frequency channels within a particular band, comprising:

injection means for generating a first injection signal at a first injection frequency;

first mixing means, having an input for accepting signals at a desired input frequency, an injection input coupled to said injection means for receiving said injection signal, and an output for providing a signal at a first intermediate frequency, wherein said first injection frequency and said desired input frequency are both integer multiples of said first intermediate frequency for any and all of said channels in said frequency band;

tunable filtering means, coupled to said output of said first mixing means, for filtering said first intermediate frequency signal; and

filter control means, responsive to said injection means, coupled to said tunable filter means, for controlling the center frequency of said tunable filtering means so that said center frequency is set equal to said first intermediate frequency and said first intermediate frequency signal is appropriately filtered for any and all channels in said frequency band.

17. The superheterodyne receiver system of claim 16, wherein said integer multiples include integers having values between two and eight.

18. The superheterodyne system of claim 16 wherein;

said system includes a second mixing means, having an input for accepting signals from said output of said filtering means, an injection input, an output for providing a signal at a second intermediate frequency.

19. The superheterodyne system of claim 18,

wherein said injection means further includes second injection signal means for generating a second injection signal at a second injection frequency, said second injection signal means connected to said injection input of said second mixing means.

20. The superheterodyne system of claim 19, wherein said input frequency to said first mixing means, said first and second intermediate frequencies, and said first and second injection frequencies are an integer multiple of said second intermediate frequency for any and all of the channels within said frequency band.

21. The superheterodyne system of claim 20, further including an integrated circuit, wherein said first and second mixing means, said injection means, said tunable filter, and said control means substantially reside in said integrated circuit.

22. The superheterodyne system of claim 20, wherein said tunable filtering means has appropriate characteristics to provide protection against image frequency spurious response.

23. The superheterodyne system of claim 16, further including an integrated circuit and wherein said first mixing means and said injection means substantially resides in said integrated circuit.

24. The superheterodyne system of claim 16, wherein said tunable filtering means has appropriate characteristics to provide adequate adjacent channel selectivity.