Radio frequency transmitter and method therefor
AssigneeCrestCom, Inc.
InventorRonald McCallister
Life of this patent
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Abstract
An RF transmitter (10) is configured to transmit either wideband multichannel modulations or narrowband multichannel modulations in a variety of licensed frequency bands (70) using a single set of hardware. For narrowband modulations, a digital IF upconversion stage is performed so that, after upconversion to RF, image signals 74 are sufficiently displaced from the licensed frequency band (70) so as to be filtered off. For wideband modulations, no IF modulation stage occurs, and a direct upconversion takes place from baseband to RF. LO leakage is cancelled using a negative feedback loop that combines a digital DC signal with a communication signal (26, 52) prior to a direct or final analog upconversion stage (62).
Claims35
A radio-frequency (RF) transmitter comprising:
- a digital communication signal source configured to supply a data stream conveying a plurality of channels separated in frequency from one another in said data stream and exhibiting a baseband center frequency (FBB) for all of said plurality of channels which is less than a bandwidth that spans all of said channels;
- a digital mixer coupled to said communication signal source and configured to shift said plurality of channels in frequency so that an intermediate frequency (IF) center frequency (FIF) for all said channels is greater than said bandwidth that spans all of said channels;
- a digital-to-analog converter coupled to said digital mixer;
- an analog upconverter coupled to said digital-to-analog (D/A) converter;
- and
- a power amplifier coupled to said analog upconverter.
A radio-frequency (RF) transmitter comprising:
- a communication signal source configured to supply a communication signal modulated with user-supplied data;
- an upconverter coupled to said communication signal source and configured to generate an RF form of said communication signal, said RF form of said communication signal having a local oscillator (LO) leakage component therein;
- a combiner coupled to said upconverter;
- a power amplifier adapted to amplify said RF form of said communication signal for broadcast from said RF transmitter;
- a downconverter adapted to receive a portion of said RF form of said communication signal and to produce a return baseband signal from said portion;
- and
- an LO leakage detector coupled to said downconverter and to said combiner, said LO leakage detector being configured to generate a combining signal in response to said RF form of said communication signal which, when combined with said communication signal in said combiner, at least partially cancels said LO leakage component.
A method of operating a radio-frequency (RF) transmitter comprising:
- determining whether or not said transmitter will transmit a narrowband communication signal;
- providing a baseband digital data stream which conveys a plurality of channels separated in frequency from one another and which exhibits a baseband center frequency (FBB) for all of said plurality of channels that is less than a bandwidth that spans all of said channels;
- when said determining activity determines that said transmitter will transmit a narrowband communication signal:
- digitally shifting said plurality of channels in frequency to produce an intermediate frequency (IF) digital data stream for which an IF center frequency (FIF) is greater than said bandwidth that spans all of said channels;
- converting said IF digital data stream into an analog IF communication signal;
- and
- upconverting said analog IF communication signal to a radio-frequency (RF) communication signal having an RF center frequency (FRF).
Dependencies are inferred from the claim text.