Mobile radio transmitter with normal and talk-around frequency bands

• US 6,091,939 A
• Filed: 02/18/1997
• Issued: 07/18/2000
• Est. Priority Date: 02/18/1997
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Banh, An Tuyen
• Primary Examiner(s): Tsang, Fan
• Assistant Examiner(s): Tran, Congvan
• Application Number:
  US08/800,450
• Time in Patent Office: 1,246 Days
• Field of Search: 455/102, 455/103, 455/118, 455/517, 455/550, 455/552, 455/553, 375/261, 375/262
• US Class Current: 455/102
• CPC Class Codes: H03D 7/161 all the frequency changers being connected in cascade
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes

Abstract

A transmitter circuit for use in a mobile radio using both a normal frequency transmission band and a talk-around frequency transmission band is disclosed. The transmitter employs a local oscillator in the modulation circuit that operates at only a single frequency band characteristic. At the output of the modulation circuit, one of two transmission paths is selected by an RF switch. In the normal transmission path, the input signal is output in the normal frequency band. Alternatively, in the talk-around transmission path, the input signal is modulated to the talk-around frequency band and then output. The present circuitry eliminates the requirement for local oscillators having dual operational characteristics.

Claims

1. A transmitter for communicating with a remote mobile radio directly to the mobile radio at a talk-around frequency range or through a common base station at a normal frequency range, comprising:

a switch to select one of the talk-around or normal frequency ranges;

a modulator to input a desired signal, modulate the desired signal, and output the modulated desired signal as an intermediate signal;

a first transmission path, communicating with the modulator through the switch, to input the intermediate signal and to output the intermediate signal at the normal frequency range to the mobile radio, when the switch selects the normal frequency range;

a second transmission path, independent of the first transmission path, communicating with the modulator through the switch, to input the intermediate signal, modulate the intermediate signal to the talk-around frequency range, and output the intermediate signal at the talk-around frequency range to the common base station, when the switch selects the talk-around frequency range;

a transmission antenna to receive the intermediate signal at said one of the talk-around or normal frequency ranges from a corresponding one of the first or second transmission paths, and to transmit the received intermediate signal to a corresponding one of said base station and mobile radio.

2. A transmitter according to claim 1, wherein the first transmission path inputs the intermediate signal, modulates the intermediate signal to the normal frequency range, and outputs the intermediate signal at the normal frequency range.

3. A transmitter according to claim 1, wherein the modulator modulates the desired signal to the normal frequency range.

4. A transmitter according to claim 3, wherein one of said first and second transmission paths corresponding to said selected one of the talk-around and normal frequency ranges inputs the intermediate signal at the normal frequency range.

5. A transmitter according to claim 1, wherein:

the modulator modulates the desired signal to a third frequency range and outputs the modulated desired signal as the intermediate signal at the third frequency range;

the first transmission path inputs the intermediate signal at the third frequency range, modulates the intermediate signal to the normal frequency range, and outputs the intermediate signal at the normal frequency range, when the switch selects the normal frequency range; and

the second transmission path inputs the intermediate signal at the third frequency range, modulates the intermediate signal to the talk-around frequency range, and outputs the intermediate signal at the talk-around frequency range, when the switch selects the talk-around frequency range.

6. A transmitter according to claim 1, wherein the modulator outputs the intermediate signal at the same frequency range to the first transmission path, when the switch selects the normal frequency range, as to the second transmission path, when the switch selects the talk-around frequency range.

7. A transmitter according to claim 6, wherein the modulator outputs the intermediate signal at the same normal frequency range.

8. A transmitter having a normal transmission mode in which a transmission signal is transmitted in a normal frequency band and a talk-around transmission mode in which the transmission signal is transmitted in a talk-around frequency band, comprising:

a modulation circuit to modulate an input signal to produce the transmission signal in the normal frequency band; and

a band select circuit having a normal transmission path, a talk-around transmission path, and an RF switch coupling the modulation circuit to the normal transmission path and the talk-around transmission path,

said normal transmission path outputting the transmission signal from the modulation circuit in the normal frequency band; and

said talk-around transmission path having a talk-around frequency mixer and a fixed frequency local oscillator to modulate the signal output by the modulation circuit with a signal from the local oscillator to produce the transmission signal at a frequency in the talk-around frequency band.

9. A transmitter according to claim 8, wherein:

the modulation circuit includes;

an IF local oscillator operating at an intermediate frequency;

an I&

Q modulator to accept the input signal and modulate the input signal with a signal from the IF local oscillator;

a second mixer to accept the signal output by the I&

Q modulator; and

a main local oscillator inputting a signal to the mixer to produce the transmission signal.

10. A transmitter according to claim 9, wherein the main local oscillator inputs the signal to the mixer at the normal frequency range incremented by the intermediate frequency.

11. A transmitter according to claim 9, wherein the main local oscillator is not in a feedback loop.

12. A transmitter according to claim 9, wherein the main local oscillator operates at the same frequency band to provide the when the RF switch couples the modulation circuit to the normal transmission path as when RF switch couples the modulation circuit to the talk-around transmission path.

13. A transmitter according to claim 9, wherein the main local oscillator inputs a signal to the second mixer to produce the transmission signal in only the normal frequency band.

14. A transmitter according to claim 8, wherein the modulation circuit includes a first stage having a modulator and an IF local oscillator to modulate the input signal to an intermediate frequency, and a second stage having a second mixer and a main local oscillator operating at a frequency in a range equal to the normal frequency range plus the IF local oscillator frequency.

15. A transmitter according to claim 14, wherein the main local oscillator operates only at a frequency in a range equal to the normal frequency range plus the IF local oscillator frequency.

16. A transmitter, comprising:

an I&

Q modulator inputting I/Q input signals;

an IF local oscillator operating at an intermediate frequency and providing an intermediate frequency signal to the I&

Q modulator for modulation with the I/Q input signals;

a first filter connected to an output of the I&

Q modulator;

a first mixer connected to an output of the first filter;

a main local oscillator providing an RF signal to the first mixer to create a transmission signal in a normal frequency band;

a second filter connected to an output of the first mixer;

a normal transmission path; and

a talk-around transmission path different from the normal transmission path, including;

a second mixer; and

a talk-around local oscillator providing an RF signal to the second mixer to create a transmission signal in a talk-around frequency band different from the normal frequency band; and

a third filter connected to an output of the second mixer; and

a RF switch connected to an output of the second filter, and connected to the normal transmission path and the talk-around transmission path to connect one of said paths to the output of the second filter.

17. A method of transmitting desired signals in a selected one of two different frequency bands, comprising the steps of:

1) modulating the desired signal to an intermediate frequency;

2) mixing the signal from step

     1) with a main local oscillator signal in a frequency band equal to one of the two different frequency bands incremented by the intermediate frequency;

3) switching the signal from step

     2) to either a normal transmission path or a talk-around transmission path;

4) if in step

     3), the signal from step

     2) is switched to the normal transmission path, amplifying the signal from step

     2), and then outputting the signal at said one of the two different frequency bands;

5) if in step

     3), the signal from step

     2) is switched to the talk-around transmission path, modulating the signal from step

     2) to the other of said two different frequency bands, amplifying the modulated signal, and then outputting the amplified signal at said other of said two different frequency bands.

18. A transmitter for communicating with a remote mobile radio directly to the mobile radio at a talk-around frequency range or through a common base station at a normal frequency range, comprising:

a switch to select one of the talk-around or normal frequency ranges;

a modulator to input a desired signal, modulate the desired signal, and output the modulated desired signal as an intermediate signal at an intermediate frequency range;

a first transmission path, communicating with the modulator through the switch, to input the intermediate signal at the intermediate frequency range and to output the intermediate signal at the normal frequency range to the mobile radio, when the switch selects the normal frequency range;

a second transmission path, communicating with the modulator through the switch, to input the same intermediate signal at the same intermediate frequency range, modulate the intermediate signal to the talk-around frequency range, and output the intermediate signal at the talk-around frequency range to the common base station, when the switch selects the talk-around frequency range;

a transmission antenna to receive the intermediate signal at said one of the talk-around or normal frequency ranges from a corresponding one of the first or second transmission paths, and to transmit the received intermediate signal to a corresponding one of said base station and mobile radio.

19. A transmitter according to claim 18, wherein the first transmission path inputs the intermediate signal, modulates the intermediate signal to the normal frequency range, and outputs the intermediate signal at the normal frequency range.

20. A transmitter according to claim 18, wherein the modulator modulates the desired signal to the normal frequency range.

21. A transmitter according to claim 20, wherein one of said first and second transmission paths corresponding to said selected one of the talk-around and normal frequency ranges inputs the intermediate signal at the normal frequency range.

22. A transmitter according to claim 18, wherein:

the modulator modulates the desired signal to a third frequency range and outputs the modulated desired signal as the intermediate signal at the third frequency range;

the first transmission path inputs the intermediate signal at the third frequency range, modulates the intermediate signal to the normal frequency range, and outputs the intermediate signal at the normal frequency range, when the switch selects the normal frequency range; and

the second transmission path inputs the intermediate signal at the third frequency range, modulates the intermediate signal to the talk-around frequency range, and outputs the intermediate signal at the talk-around frequency range, when the switch selects the talk-around frequency range.

23. A transmitter according to claim 18, wherein the modulator outputs the intermediate signal at the same frequency range to the first transmission path, when the switch selects the normal frequency range, as to the second transmission path, when the switch selects the talk-around frequency range.

24. A transmitter according to claim 23, wherein the modulator outputs the intermediate signal at the same normal frequency range.