RF architecture for cellular dual-band telephones

• US 6,208,875 B1
• Filed: 04/08/1998
• Issued: 03/27/2001
• Est. Priority Date: 04/08/1998
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Damgaard, Morten, Li, Leo
• Primary Examiner(s): Eisenzopf, Reinhard
• Assistant Examiner(s): NGUYEN, DUC M
• Application Number:
  US09/057,124
• Time in Patent Office: 1,084 Days
• Field of Search: 455/76, 455/78, 455/86, 455/85, 455/84, 455/83, 455/88, 455/552, 455/553, 455/260, 455/180.3, 455/189.1
• US Class Current: 455/552.1
• CPC Class Codes: H03L 7/23 with pulse counters or frequency dividers
• CPC Class Codes: H04B 1/005 adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
• CPC Class Codes: H04B 1/0057 using diplexing or multiplexing filters for selecting the desired band
• CPC Class Codes: H04B 1/006 using switches for selecting the desired band H04B1/0057 takes precedence
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes

Abstract

A dual band RF architecture including a GSM quadrature modulator for modulating an intermediate frequency (IF) wherein the frequency of the modulated IF signal is changed such that one IF is used for the GSM band and another IF is used for the DCS 1800 band. An intermediate frequency (IF) filter with a pass band that covers both the GSM IF and the DCS 1800 IF is connected to the output of the modulator and outputs to a transmit phase lock loop, which translates the IF signal from the IF filter to either a DCS 1800 band radio frequency signal or a GSM band radio frequency signal, depending on the frequency of a local oscillator (LO). The receiver employs a down converter which provides a down converted output signal selected by high side injection for the GSM band an by low side injection for the DCS 1800 band. The down converter outputs to an intermediate frequency (IF) receiver filter centered at 400 MHz designed to pass either the down converted GSM signal or the down converted DCS signal to demodulation circuitry. A single phase lock loop circuit is used to supply, on a single output, the LO signal for down converting either the GSM receive band or the DCS 1800 receive band, as well as the LO for the transmit phase lock loop.

Claims

1. An RF dual band phone circuit operating in the DCS 1800 and GSM frequency bands, comprising:

a modulator for producing an output comprising a pair of baseband signals (I and Q) modulating a first intermediate frequency (IF) signal for the GSM band or a second intermediate frequency (IF) signal for the DCS 1800 band;

a receive phase lock loop for generating a high side injection local oscillator signal for the GSM band and a low side injection local oscillator signal for the DCS 1800 band;

a transmit phase lock loop for translating the first IF signal to a GSM band radio frequency signal or the second IF signal to a DCS 1800 band radio frequency signal, depending on which one of the two local oscillator signals is supplied to it, the GSM band signal or the DCS 1800 band signal being down converted and fed back to the IF input of the transmit phase lock loop; and

an amplifier for amplifying the output of the transmit phase lock loop and for supplying the amplified signal to an antenna.

2. The circuit of claim 1 further including a down converter connected to the receive phase lock loop for receiving one of a GSM band signal and a DCS 1800 band signal and for down converting the received GSM band signal with the high side injection local oscillator signal and the received DCS 1800 band signal with the low side injection local oscillator signal.

3. The circuit of claim 2 further including an intermediate frequency (IF) receiver filter centered at 400 MHz having an input connected to the output of the down converter.

4. The circuit of claim 2 wherein the high and low side injection local oscillator signal lie within a frequency range of 1284 MHz to 1480 MHz.

5. The circuit of claim 3 further including a filter positioned before the down converter for providing at least 20 db attenuation of the GMS and DCS image frequencies.

6. The circuit of claim 1 wherein the first IF frequency is 394 MHz and the second IF frequency is 378 MHz.

7. The circuit of claim 1 wherein the receive phase lock loop includes a single voltage controlled oscillator for generating both local oscillator signals.

8. The circuit of claim 7 wherein both local oscillator signals lie within a frequency range of 1284 MHz to 1480 MHz.

9. The circuit of claim 1 wherein the transmit phase lock loop includes a mixer for mixing the GMS band radio frequency signal with the high side injection local oscillator signal and the DCS 1800 radio frequency band signal with the low side injection local oscillator signal, and a bandpass filter for removing unwanted mixing products form the mixer output.

10. The circuit of claim 9, wherein the transmit phase lock loop includes a first frequency divider for dividing the frequency of one of the first and second IF signal and a second frequency divider for dividing the frequency of the bandpass filter output signal, and a phase detector for comparing the phases of the frequency divided signals.

11. The circuit of claim 10, wherein the first and second frequency divider divide the frequency by 2.

12. The circuit of claim 1 further comprising a single IF VCO, and a frequency divider connected to the output of the IF VCO for generating an IF frequency signal for the modulator.

16. The circuitry of claim 1 wherein said intermediate frequency filter is a IF frequencies.

13. An RF dual band phone circuit operating in the DCS 1800 and GSM frequency bands comprising:

a modulator for producing an output comprising a pair of baseband signals (I and Q) modulating a first intermediate frequency (IF) signal for the GSM band or a second intermediate frequency (IF) signal for the DCS 1800 band;

an intermediate frequency (IF) filter having an input and an output, the input of the filter being connected to the output of the modulator;

a transmit phase lock loop connected to the output of the IF filter for translating the filtered first IF signal to a GSM band radio frequency signal or the filtered second IF signal to a DCS 1800 band radio frequency signal, depending on which one of a first and second local oscillator signal is supplied to it the GSM band signal or the DCS 1800 band signal being down converted and fed back, to the IF input of the transmit phase lock loop;

an amplifier for amplifying the output of the transmit phase lock loop;

a down converter for receiving one of a GSM band signal and a DCS 1800 band signal and for supplying a down converted output signal, said output signal being selected by high injection for the GSM band and low side injection for the DCS 1800 band; and

a local oscillator (LO) phase lock loop for supplying, on a single output, either the first LO frequency signal or the second LO frequency signal to the down converter and to the transmit phase lock loop for effecting a down conversion in the transmit phase lock loop of the GSM band or DCS 1800 band radio frequency signal, whereby a common phase lock loop is used for down conversion in both the transmit and receive paths of the circuit.

14. The circuit of claim 13 further including

a single IF VCO, and

frequency divider means connected to the output of the IF VCO for generating an IF frequency signal for the modulator, and an IF frequency for a demodulator.

15. The circuit of claim 14 further including

an intermediate frequency (IF) filter centered at 400 MHz having an input connected to the output of the down converter.

17. The circuit of claim 14, wherein the single IF VCO is tunable over a frequency range of 756 MHz to 800 MHz.

18. The circuit of claim 17 wherein the first phase lock loop further includes a single voltage controlled oscillator having a frequency range of 1284 MHz to 1480 MHz for generating both the high and low side injection local oscillator signal.

19. A method for generating a dual band RF output in an RE dual band phone operating in the DCS 1800 and GSM frequency band, the steps of the method comprising:

modulating a first intermediate frequency (IF) signal for the GSM band on a second intermediate frequency (IF) signal for the DCS 1800 band with a pair of baseband signals (I and Q);

generating a high side injection local oscillator signal for the GSM band and a low side injection local oscillator signal for the DCS 1800 band;

translating the first IF signal to a GSM band radio frequency signal using the high side injection local oscillator signal;

translating the second IF signal to a DCS 1800 band radio frequency signal using the low side injection local oscillator signal; and

down converting the GSM band signal or the DCS 1800 signal and feeding it back to the IF signal translating steps as part of a phase lock loop.