Digital modulator for a GSM/GPRS/EDGE wireless polar RF transmitter

• US 7,860,188 B2
• Filed: 02/24/2009
• Issued: 12/28/2010
• Est. Priority Date: 09/30/2003
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Jensen, Henrik T.
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Singh; Hirdepal
• Application Number:
  US12/391,630
• Publication Number:
  US 20090154598A1
• Time in Patent Office: 672 Days
• Field of Search: 375/135, 375/146, 375/215, 375219-222, 375/267, 375279-280, 375/295, 375/297, 375/308, 375/316, 375/329, 375/347, 375/354, 375/355, 375/302, 375259-260, 375/322, 455/102, 455/108
• US Class Current: 375/308
• CPC Class Codes: H04L 27/2003 for continuous phase modulation frequency shift keying H04L27/10
• CPC Class Codes: H04L 27/2017 in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation H04L27/201 takes precedence

Abstract

A digital modulator in a radio transmitter includes circuitry for switching between Gaussian Minimum Shift Keying (GMSK) and Phase-Shift Keying (PSK) while maintaining spectral mask requirements. The digital modulator of the present invention includes both GMSK and PSK symbol mappers that produce PSK in-phase and quadrature symbols and GMSK symbols, respectively, to a pulse shaping block. Based on opposite phases of a modulation control signal, the symbol mappers produce either modulated data or a steam of logic zeros to the pulse shaping block. The pulse shaping block filters the received data and multiplexes the data so that each modulated data stream receives non-zero data during a guard time to avoid abrupt changes in the modulated signal that would violate the spectral mask requirements.

Claims

1. A polar radio frequency (RF) transmitter within a radio transceiver for producing Phase Shift Keying (PSK) and Gaussian Minimum Shift Keying (GMSK) modulated communication signals, comprising:

a baseband processor for producing transmission (TX) data and a TX control signal;

a digital modulator that receives the TX data, that digitally modulates outgoing digital data to produce one of a PSK and GMSK modulated digital signal based upon the TX control signal, wherein the digital modulator further includes;

a modulation switching control block that receives the TX control signal, producing a modulation control signal to select one of a PSK modulation and GMSK modulation mode;

a PSK symbol mapper operably coupled to receive the TX data that produces in-phase and quadrature PSK symbols based on the TX data and further based on a first value of the modulation control signal and that produces logic zero signals based on a second value of the modulation control signal;

a GMSK symbol mapper operably coupled to receive the TX data that produces binary GMSK symbols based on the TX data and further based on the second value of the modulation control signal and that produces logic zero signals based on the first value of the modulation control signal;

a pulse shaping block for filtering the PSK and GMSK symbols, wherein the pulse shaping block produces filtered PSK symbols for the first value of the modulation control signal and produces filtered GMSK symbols for the second value of the modulation control signal;

envelope path adjustment circuitry operably coupled to receive the filtered PSK symbols that produces an envelope signal;

phase path adjustment circuitry operably coupled to receive the filtered GMSK symbols and a PSK phase signal that produces a phase signal;

first and second Digital-to-Analog converters (DACs) for converting the envelope signal and the phase signal, respectively, from digital signals to analog signals to produce analog envelope signal and analog phase signal;

first and second low pass filters for filtering the analog envelope signal and the analog phase signal, respectively;

translational loop operably coupled to receive the analog phase signal to up-convert the analog phase signal from an IF frequency to an RF frequency; and

a power amplifier for producing a modulated RF signal based on at least one of the analog phase signal and the analog envelope signal.

2. The polar RF transmitter of claim 1 further including a gain select block wherein the gain select block increases a gain magnitude of the GMSK symbol based on a baseband gain select signal.

3. The polar RF transmitter of claim 1 further including an envelope and phase extraction block that comprises a COordinate Rotation DIgital Computer (CORDIC).

4. A polar RF transmitter within a radio transceiver for producing Phase Shift Keying (PSK) and Gaussian Minimum Shift Keying (GMSK) modulated communication signals, comprising:

a baseband processor for producing transmission (TX) data and a TX control signal;

a digital modulator that receives the TX data, that digitally modulates outgoing digital data to produce one of a PSK and GMSK modulated digital signal based upon the TX control signal, wherein the digital modulator further includes;

a modulation switching control block that receives the TX control signal, producing a modulation control signal to select one of a PSK modulation and GMSK modulation mode;

a PSK symbol mapper operably coupled to receive the TX data that produces in-phase and quadrature PSK symbols based on the TX data and further based on a first value of the modulation control signal and that produces logic zero signals based on a second value of the modulation control signal;

a GMSK symbol mapper operably coupled to receive the TX data that produces binary GMSK symbols based on the TX data;

envelope path adjustment circuitry that produces an envelope signal based on the PSK symbols;

phase path adjustment circuitry that receives filtered GMSK symbols and PSK phase signal to produce a phase signal; and

a translational loop that up-converts the phase signal in an analog form at intermediate frequency (IF) to a radio frequency (RF) for transmission.

5. The polar RF transmitter of claim 4 further including first and second Digital-to-Analog converters (DACs) for converting the envelope signal and the phase signal, respectively, from digital signals to analog signals to produce analog envelope signal and analog phase signal.

6. The polar RF transmitter of claim 5 wherein one of the DACs produces a phase signal as an IF signal.

7. The polar RF transmitter of claim 6 wherein the phase signal, in the digital form, comprises a sample rate sufficiently high to convert to IF by the one DAC.

8. The polar RF transmitter of claim 4 further including first and second low pass filters for filtering the analog envelope signal and the analog phase signal, respectively.

9. The polar RF transmitter of claim 4 wherein the GMSK symbol mapper produces logic zero signals based on the first value of the modulation control signal.

10. The polar RF transmitter of claim 4 further including a pulse shaping block for filtering the PSK and GMSK symbols, wherein the pulse shaping block produces filtered PSK symbols for the first value of the modulation control signal and produces filtered GMSK symbols for the second value of the modulation control signal.

11. The polar RF transmitter of claim 4 further including a power amplifier that produces a modulated RF signal based on the RF frequency analog phase signal and the analog envelope signal.

12. The polar RF transmitter of claim 4 wherein the phase path adjustment circuitry produces a phase signal based on the GMSK symbols and further based upon the PSK phase signal.

13. The polar RF transmitter of claim 4 further including an envelope magnitude and group delay equalizer block that pre-distorts the envelope signal to substantially compensate for expected distortion in an analog portion of an envelope path.

14. The polar RF transmitter of claim 4 further including an envelope and phase mismatch cancellation block for substantially canceling a timing mismatch between the envelope and a phase path.

15. The polar RF transmitter of claim 4 further including an envelope signal interpolation block that increases a sampling rate of the PSK modulated digital signal.