EP0408238A2 — A frequency synthesiser

Claim 1

Independent Claim 123 words

A frequency synthesiser comprising a phase locked loop having a reference oscillator coupled to a first input of a comparator, a voltage controlled oscillator (VCO) for providing an output signal, which output signal is fed back by way of a divider circuit for dividing the output frequency by a factor N to a second input of said comparator, the output of the comparator being applied to a control input of the VCO, and including input means for applying a modulating signal in binary format via integrator means for control of the divider circuit, and means having a predetermined transfer function coupling said modulating signal to the control input of the VCO whereby to provide a modulation of the output signal in desired format.

Claim 2

Dependent Claim 123 words

A frequency synthesiser comprising a phase locked loop having a reference oscillator coupled to a first input of a comparator, a voltage controlled oscillator (VCO) for providing an output signal, which output signal is fed back by way of a divider circuit for dividing the output frequency by a factor N to a second input of said comparator, the output of the comparator being applied to a control input of the VCO, and including input means for applying a modulating signal in binary format via integrator means for control of the divider circuit, and means having a predetermined transfer function coupling said modulating signal to the control input of the VCO whereby to provide a modulation of the output signal in desired format.

Claim 3

Dependent Claim 23 words

A synthesiser according to Claim 1 wherein the transfer function means is a Gaussian low pass filter in order to produce GMSK modulation.

Claim 4

Dependent Claim 19 words

A synthesiser according to Claim 1 wherein the transfer function means is a direct connection for producing MSK modulation.

Claim 5

Dependent Claim 52 words

A synthesiser according to any preceding claim wherein the divider circuit includes control means for producing a division factor of N or N+1, and the output of the integrator means is arranged to control the number of cycles of the divider in the N division mode relative to the N+1 division mode.

Claim 6

Dependent Claim 154 words

A frequency synthesiser comprising a phase locked loop having a reference oscillator coupled to a first input of a comparator, a VCO for providing an output signal which output signal is fed back by way of a divider circuit for dividing the output frequency by a factor N to a second input of said comparator, the output of the comparator being applied to a control input of the VCO, including input means for applying a modulating signal via integrator means for control of the divider circuit, and the modulating signal being coupled to the control input of the VCO, in order to provide a modulation of the output signal in desired format, wherein the divider circuit includes control means for producing a division factor of N or N+1, and the output of the integrator is arranged to control the number of cycles of the divider in the N mode relative to the N+1 mode.

Claim 7

Dependent Claim 154 words

A frequency synthesiser comprising a phase locked loop having a reference oscillator coupled to a first input of a comparator, a VCO for providing an output signal which output signal is fed back by way of a divider circuit for dividing the output frequency by a factor N to a second input of said comparator, the output of the comparator being applied to a control input of the VCO, including input means for applying a modulating signal via integrator means for control of the divider circuit, and the modulating signal being coupled to the control input of the VCO, in order to provide a modulation of the output signal in desired format, wherein the divider circuit includes control means for producing a division factor of N or N+1, and the output of the integrator is arranged to control the number of cycles of the divider in the N mode relative to the N+1 mode.

Claim 8

Dependent Claim 70 words

A synthesiser according to Claim 4 or 5 wherein the divider circuit includes a first counter for determining a nominal value of N, a swallow counter for controlling a prescaler circuit, the prescaler circuit being coupled to receive the output of the VCO and to divide the VCO frequency by (n) or (n+1), wherein the swallow counter determines the switching of the prescaler circuit between the (n) and (n+1) modes.

Claim 9

Dependent Claim 23 words

A synthesiser according to Claim 6 wherein the integrator means provides a control output for control of the switching of the prescaler circuit.

Claim 10

Dependent Claim 43 words

A synthesiser according to Claim 7 wherein the integrator means includes a counter which provides said control output in the form of a pulse whose length is dependant on the value of the counter and which controls the switching of the prescaler circuit.

Claim 11

Dependent Claim 37 words

A synthesiser according to any preceding claim wherein the integrator means comprises an up/down counter, the carry/borrow outputs of which are coupled to a further counter means, the output of which is coupled to the divider circuit.

Claim 12

Dependent Claim 52 words

A synthesiser as claimed in Claim 9 wherein the value of the up/down counter is applied to a circuit for producing a pulse of variable width, which is applied via scaling means to a summing device for summing with the output of said comparator for compensating for situations where N is small.

Claim 13

Dependent Claim 41 words

A synthesiser as claimed in Claim 1 or 5 including summing means for summing an input signal or the output signal of the comparator with a signal derived from the input modulation signal for compensation in situations where N is small.

A frequency synthesiser

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