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[0002] The demand for wireless communications can be said to be inversely related to the cost of providing portable radio transceivers. Hence it is preferred that such transceivers be provided substantially in an integrated circuit form to minimize cost.
[0003] A radio transceiver has two functions, one being that of broadcasting an information signal and the other being that of receiving an information signal. The two functions may occur coincidentally at different frequencies, as in full duplex operation, or the two functions may be mutually exclusive such that the function of receiving is interrupted when the broadcasting function occurs, as in simplex operation. In simplex operation, the broadcast signal can be at the same frequency as the signals being received. The transceiver is switched between the broadcast and receive functions to effect information exchange with another party either directly or via some intervening communications network. In one example the transceiver periodically switches between the broadcast and receive functions to effect exchanges of packetized data at a rates which appear to provide full duplex operation for a user.
[0004] Sophisticated transceivers based on superheterodyne principles have evolved over the years such that the weakest of recognizable signals can be usefully received and signals can be broadcast with very precise frequency and bandwidth control. One example is found in U.S. Pat. No. 5,423,076 issued Jun. 6, 1995 to Larry L. Westergren et al, titled “Superheterodyne Transceiver with Bilateral First Mixer and Dual Phase Locked Loop Frequency Control”. The receive function is performed by circuitry which includes triple down conversion, requiring local oscillators, mixers and attendant bandpass filters for a receive frequency band as well as each of three successively lower intermediate frequencies.
[0005] In U.S. Pat. No. 6,006,081 titled “Communications Receivers” and issued Dec. 21, 1999, Paul A. Moore discloses an integrated zero IF receiver which receives an input signal and down converts it to substantially zero intermediate frequency quadrature related signals (I, Q). In one example the received signal is supplied to a pair of mixers. A local oscillator signal is supplied to one of the mixers directly and a phase shifted version of the local oscillator signal is supplied to the other of the mixers. The products of mixing from the one mixer are applied to a first lowpass filter which passes an in-phase difference signal (I) a demodulator. The products of mixing from the other mixer
[0006] The examples disclosed by Moore and Westergren et al are generally representative of the field of radio apparatus in that each requires a plurality of filters which can be difficult if not impossible to provide in integrated circuit form. Provision of such in discrete form with the required interconnections adds significantly to the expense of manufacture of small portable radio devices such as receivers and transceivers.
[0007] It is an object of the invention to provide a frequency modulation radio with direct conversion wherein a local oscillator signal is generated having a frequency within a preselected frequency range and the frequency being varied in response to a variable low frequency signal; the local oscillator signal is mixed with a received signal to provide a baseband signal and the variable low frequency signal is generated by a controlled oscillator in inverse relationship to a direct current component in said baseband signal.
[0008] It is also an object of the invention to provide a direct conversion transceiver which is economically producible with an integrated circuit manufacturing technology.
[0009] In accordance with an aspect of the invention, in a direct conversion transceiver, a local oscillator signal is generated from a variable low frequency signal produced by a controlled oscillator. In a receive mode, a local oscillator signal is mixed with a received signal to produce difference signal including a base band signal. The controlled oscillator is responsive to received baseband signals for varying the frequency of the variable low frequency signal and consequently the frequency of the local oscillator signal, and, in a transmit mode the controlled oscillator is responsive to transmit baseband signals for varying the frequency of the variable low frequency signal and consequently the frequency of the local oscillator signal.
[0010] Also in accordance with an aspect of the invention an FM transceiver being alternately operable in receive and broadcast modes, comprises: a mixer responsive to received and local signals for generating difference signals; a local oscillator for generating said local signal with a frequency substantially the same as a centre frequency of a signal intended for reception and being responsive to the difference signals received for deviating the frequency of the local signal toward the centre frequency of a signal being received, whereby when said signal being received is substantially the signal intended for reception, a difference between said centre frequency and the local signal frequency approaches 0 Hertz, the local oscillator also for generating said local signal with a frequency substantially the same as a centre frequency of a signal intended for broadcast and being responsive to signals representing information intended for broadcast for deviating the frequency of the local signal away from the centre frequency to provide a frequency modulated signal intended for broadcast.
[0011] In accordance with a further aspect of the invention a radio transceiver is alternately operable in receive and broadcast modes and includes a mixer responsive to received and local signals for generating received baseband signals, a local oscillator responsive to the received baseband signals for generating said local signal with a frequency substantially the same as a centre frequency of the received signal whereby said centre frequency is direct converted to substantially zero Hertz, a lowpass filter coupled in series between the mixer and the local oscillator for substantially suppressing alternating current signals of frequencies higher than a highest frequency a baseband signal intended for reception. In the broadcast mode, the local oscillator is responsive to transmit baseband signals representing information for broadcast, for frequency modulating the local signals to produce frequency modulated local signals, and the transceiver further includes an output amplifier being controllable to be responsive to the frequency modulated local signals for generating a power signal for broadcasting.
[0012] In an example which embodies the invention, a radio transceiver is operable in a broadcast mode for broadcasting signals being frequency modulated with originating information signals coupled thereto via an input port and alternately the radio transceiver is operable in a receive mode for receiving frequency modulated signals and deriving therefrom received information signals for supply to an output port. The radio transceiver comprises: an oscillator for generating an alternating current signal In the broadcast mode, the oscillator is responsive to signals at the input port for generating the alternating current signal with deviations of frequency representative said originating information signals. In the receive mode the oscillator is responsive to signals supplied to the output port for generating the alternating current signal with a frequency proportional to a carrier frequency of a received signal. In both modes, a controlled up converter is responsive to the alternating current signal from the oscillator for generating a local signal having a preselected frequency being modulated by said alternating current signal. In the broadcast mode, a broadcast amplifier amplifies the local signal to provide a broadcast signal. In the receive mode, a radio frequency amplifier receives radio frequency signals to produce received radio signals. A mixer is responsive to the received radio signals and the local signal for generating a mixed signal including difference signal components. A lowpass filter has a passband width of a maximum frequency substantially corresponding to a maximum deviation of frequency of any radio signal intended for reception. The lowpass filter is coupled between the mixer and the output port so that the difference signals from the mixer are passed to the output port.
[0013] In one example the controlled up converter comprises: a phase shifter having first and second outputs and being responsive to the alternating current signal from the oscillator for providing a pair of signals related in quadrature phase, the signal from the second output lagging the signal from the first output; a channel selector for generating any of a plurality of predetermined radio frequency signals at first and second outputs and being related in quadrature phase, the radio frequency signal from the second output lagging the radio frequency signal from the first output; a first balanced mixer having inputs coupled to the first outputs of the phase shifter and the channel selector and an output for providing first mixed signals; a second balanced mixer having inputs coupled to the second outputs of the phase shifter and the channel selector and an output for providing second mixed signals; and an adder for generating said local signal by summing said first and second mixed signals.
[0014] In accordance another aspect of the invention, a method of operating a radio transceiver to alternately receive and broadcast radio frequency signals comprises the steps of:
[0015] a) generating a local signal of a frequency similar to a radio frequency signal intended for reception and for broadcast;
[0016] b) mixing received signals with the local signal to generate mixed signals including a difference signal;
[0017] c) deriving a baseband signal by suppressing any mixed signals being of frequencies greater than a maximum bandwidth of frequency modulation information intended for reception;
[0018] d) continuously generating an alternating current signal;
[0019] e) adjusting a frequency of the alternating current signal in response to a direct current component of the base band signal and responsive to the adjusted frequency altering the frequency of the local signal being generated in step a) in response to the frequency of the alternating current signal, whereby the frequency of the local signal is more closely similar to the frequency intended for reception; and
[0020] f) while broadcasting radio frequency signals, frequency modulating said alternating current signal with frequency deviations representing information for broadcast and altering the frequency of the local signal being generated in step a) accordingly, whereby the local signal is a frequency modulated signal for broadcasting.
[0021] An example embodiment is discussed with reference to the accompanying drawings in which:
[0022]
[0023]
[0024] In
[0025] In
[0026] The FM transceiver includes a radio frequency (RF) amplifier
[0027] The local oscillator
[0028] Switches
[0029] More specifically, in the receive mode of operation, the local oscillator signal from the adder limiter circuit
[0030] In the broadcast mode of operation the break element of the switch
[0031] Information signals intended for broadcast can be supplied directly to the input of the VCO
[0032] It is envisaged that the FM transceiver in accordance with an architecture as generally described herein is advantageously manufactured as an integrated circuit structure. In view of the preceding disclosure, various examples of radio transceiver apparatus and methods for operation of radio transceiver apparatus will become apparent to persons skilled in the radio arts and in integrated circuit design. Such examples should be understood to be within the spirit of the invention, the scope of which is of record in the appended claims.