Abstract: An analogue-to-digital converter arrangement including a signal de-emphasis network 10.sub.I, 10.sub.Q which attenuates higher frequency analogue signals relative to lower frequency analogue signals, an A/D converter 11.sub.I, 11.sub.Q to which the de-emphasised signals are applied, and a pre-emphasis network 12.sub.I, 12.sub.Q substantially complementary to the de-emphasis network to which the digitised signals are applied.

Abstract: A radio receiver for frequency modulated signals in which direct conversion techniques are used to provide zero I.F. quadrature baseband signals I & Q. The I & Q signals are limited (11,12) to form square wave signals and pulse forming networks (13,14) derive pulse sequences the frequencies of which represent the polarity changes in the square wave signals. Each square wave is multiplied (15,16) by the pulse sequence derived from the other square wave to produce a unipolar pulse train. The two unipolar pulse trains are combined (17) to give a digital output signal the frequency of which is equal to the sum of the frequencies of the two pulse trains. Low pass filtering the output signal produces a simulation of the original baseband modulation.

Abstract: A direct conversion receiver in which the quadrature I and Q signals are converted into pulse density modulated digital data streams by delta-sigma modulators 14, 15. The resultant digital data streams are then processed in a logic block 18 according to predetermined logic truth tables. The digital output of the processor 18 is then converted back to an analogue signal.

Abstract: A demodulator logic for FSK signals on an RF carrier in a direct conversion radio receiver, wherein the received signals are mixed with a local oscillator to provide quadrature baseband signals, characterized in that the demodulator logic comprises two clocked D-type flip-flops, FF1,FF2 one baseband signal being applied direct to the clock input CK of one flip-flop and inverted to the clock input CK of the other flip-flop, the second baseband signal being applied to the D inputs of both flip-flops, one input Q from one flip-flop being algebraically combined with one output Q from the other flip-flop to provide a demodulator signal output of the receiver, the two flip-flop outputs being chosen so that for a given FSK value they always have the same logic value.

Abstract: A multichannel duplex radio system for cordless telephone in which digital information is sent between the two ends. The data is divided into blocks which are transmitted in a fraction of the original block length. The other time slots are used for the duplex return path and for other similar equipment operating nearby. A direct conversion radio receiver is used in which the local oscillator signal is modulated for transmission.

Abstract: A radio receiver for FM signals having a demodulation system to produce an approximation to an analog output by either measuring the time intervals between successive zero crossings in the I.F. (FIG. 1, FIG. 2B) or by filtering pulses produced at each zero crossing of the I.F. (FIG. 1, FIG. 2A). The demodulator includes two signal pathways in quadrature phase relation, the second signal either lagging or leading the first signal in dependence on whether the received signal frequency is above or below a local oscillator frequency. The modulation frequency can carry analog information separate and apart from the on-off (digital) information.

Abstract: A method of synchronizing a digital radio pager receiver with incoming digital data signals. At switch-on the receiver first attains a "course" bit synch during the first quarter-word period and then a "fine" bit synch during the next half-word period. The receiver then examines incoming data bits to determine simultaneously (a) whether valid data is being received and (b) whether the incoming data contains a preamble sequence. If either determination is successful the incoming data is then examined to determine whether it contains a synchronizing word or an address word. The synchronization and address word determination is also carried out while bit synch is obtained and the valid data/preamble determination is effected.

Abstract: A gallium arsenide logic circuit which forms part of a silicon/gallium arsenide logic interface, is provided with a negative supply voltage from a silicon logic gate whose output is held in its LOW condition. This obviates the need to provide separate power supplies to the two different semiconductor types.

Abstract: A single channel duplex transmitter/receiver utilizing digital frequency shift keying (FSK) signals. An analogue-to-digital converter frequency modulates the output of a local oscillator whose output is coupled via a mixer/combiner/splitter network to an aerial. FSK signals received from the aerial in the receiver are mixed with the local oscillator output in network to provide quadrature signals which are low-pass filtered before being demodulated in a zero IF demodulator to give a digital output. To avoid unwanted sidetone the output of the A/D converter is fed through a delay to a digital network where it is subtracted from the corresponding signals fed back through the demodulator. The digital signals are then fed to a D/A converter.

Abstract: A radio receiver for frequency shift keyed signals of the zero I.F. type. The quadrature outputs of mixers are low-pass filtered and a 90.degree. phase shift at the baseband frequency is introduced in one signal path. The baseband signals are then fully limited and applied to a logic network to provide a digital output indicative of the relative lead/lag condition of the two signal paths. The logic network can conveniently be an EXCLUSIVE-OR gate.

Abstract: A radio receiver employing paired signal paths with frequency shift keying. In each signal path pair in which demodulated signals in quadrature are produced, the outputs of the limiting amplifiers are connected to two pairs of flip-flops so that the phase changes in the amplifier outputs are indicated. The outputs of the flip-flops are selectively summed in two gates to drive the inputs of a further flip-flop the output of which is the decoded output signal.

Abstract: A dual splitter/combiner network for a single channel duplex radio transmitter/receiver has a length of transmission line 1/8 wavelength electrical length at the carrier frequency with a diode detector connected thereto at each end. A local oscillator, which is frequency modulated in the transmit mode, is connector to one end of the transmission line and an antenna to the other end. Signals from the antenna, in the receive mode, mix with the oscillator output and the difference frequency output signals at each detector will be in quadrature, suitable for subsequent processing in a direct conversion (zero I.F.) receiver circuit. In the transmit mode the frequency modulated local oscillator signal is transmitted from the antenna.

Abstract: A radio receiver for frequency modulated (FM) tones. Received signals are split and one split portion of the signal is phase shifted relative to the other and mixed with a local oscillator. The signal as received clocks a flip-flop. The phase shifted signal is fed to the switching input of the flip-flop. The input signal having been modulated with an FM tone which oscillates about the frequency of the local oscillator, the output of the flip-flop is a digital waveform the frequency of which is the same as that of the modulating tone. This digital waveform is applied to a band pass filter accepting the fundamental frequency of the digital wave form from the flip-flop for passage to a detector.

Abstract: A transmitter receiver which can be used for a cordless telephone using radio communication. The receiver produces direct conversion from the radio frequency. Local oscillator frequency is modulated by an audio signal to be sent, the modulated signals being passed through a dual splitting and combining network. The splitting network has directional properties for duplex operation. The receiver processes the signals through a differential amplifier to cancel unwanted signals.

Abstract: A simple radio receiver for FSK signals as used in a paging system. RF signals from the aerial are mixed in two high gain mixers with local oscillator signals which are in quadrature and which are at the nominal center frequency of the input signal. The output from the mixers are low-pass filtered so as to extract the difference frequency. The low-pass filter bandwidth is equal to the sideband width of the RF signal. Baseband signals from the filters are now amplified in high gain limiting amplifier stages which deliver fully symmetrically limited outputs at logic level to a D-type flip-flop.