Abstract: An FLL circuit having a capability of configuring a desired loop bandwidth in a short period of time is provided. An FDC 17 generates a feedback of an output signal of a VCO 15. An error detector 11 detects an error of the output signal of the VCO 15. A voltage retainer 13 retains an output of a control voltage of the VCO 15. A reference signal generator 16 generates a reference signal. An adder 14 adds the reference signal to a control voltage outputted by the voltage retainer 13. A Kv calculator 18 calculates a gain Kv of the VCO 15 based on a degree of transition of an output frequency of the VCO 15. A loop bandwidth controller 19 adjusts, based on the gain Kv of the VCO 15, a gain of a loop filter 12 to an optimum value, and configures a desired loop bandwidth.

Abstract: Disclosed are embodiments of a phase control circuit with an analog phase controller that is able to effectively generate control signals for all four quadrants of phase control operation.

Abstract: Techniques for achieving linear operation for a phase frequency detector and a charge pump in a phase-locked loop (PLL) are described. The phase frequency detector receives a reference signal and a clock signal, generates first and second signals based on the reference and clock signals, and resets the first and second signals based on only the first signal. The first and second signals may be up and down signals, respectively, or may be down and up signals, respectively. The phase frequency detector may delay the first signal by a predetermined amount, generate a reset signal based on the delayed first signal and the second signal, and reset the first and second signals with the reset signal. The charge pump receives the first and second signals and generates an output signal indicative of phase error between the reference and clock signals.

Abstract: A signal adjusting system includes: a signal generating device for generating a plurality of output signals according to a plurality of pre-output signals, a plurality of signal transmitting paths being coupled to the signal generating device for transmitting the plurality of output signals; and a controlling device coupled to the plurality of signal transmitting paths for receiving a first transmitted signal corresponding to a first output signal and a second transmitted signal corresponding to a second output signal, and detecting a phase different between the first transmitted signal and the second transmitted signal to generate a detected result to the signal generating device, wherein the signal generating device adjusts the phase difference between the first output signal and the second output signal according to the detected result.

Abstract: Systems, algorithms, circuits, and methods for pattern detection of signature events in signal dynamics defined by instantaneous states of applied square-wave signals. Selected patterns may be recognized individually or in equivalence classes, and detection may be implemented via state or transition analysis. Varieties of conditions may be detected in parallel, including phase, ambiguity states, and frequency comparison. One embodiment realizes a real-time frequency comparator for asynchronous square-wave signals. Realizations detect various classes of symmetry conditions unique to enveloping events occurring for these classes of square-wave signal pairs. This approach provides feedback-free implementations operating over an extremely wide frequency range and does not require signals of quadrature form. A typical logic circuit implementation involves two to four flip-flops, or two-stage two-bit shift registers, and modest combinational logic.

Abstract: Phase locked loop circuitry operates digitally, to at least a large extent, to select from a plurality of phase-distributed candidate clock signals the signal that is closest in phase to transitions in another signal such as a clock data recovery (“CDR”) signal. The circuitry is constructed and operated to avoid glitches in the output clock signal that might otherwise result from changes in selection of the candidate clock signal. Frequency division of the candidate clock signals may be used to help the circuitry support serial communication at bit rates below frequencies that an analog portion of the phase locked loop circuitry can economically provide. Over-transmission or over-sampling may be used on the transmit side for similar reasons.

Abstract: A system and method for effectively supporting a data transmission procedure includes a phase-locked loop with a phase detector that compares a clock signal and input data to generate a phase error signal for adjusting the clock signal that is generated from a voltage-controlled oscillator. The phase detector includes a positive-edge detector circuit that generates an edge detection signal P to indicate whether data transitions are present in the input data. The phase detector also includes a lead/lag indicator circuit that generates a lead/lag indicator signal T to indicate whether the clock signal is early or late with respect to the input data.

Abstract: A PLL is provided with an optimum operating point in order to have appropriately a frequency margin and a locking time. There is provided a phase looked loop which includes: a frequency divider for dividing an output signal by a dividing integer corresponding to an input code; an encoding unit for encoding the input code to generate an encoded code; and a loop filtering unit configured to adjust elements in response to the encoded code.

Abstract: Circuits, architectures, a system and methods for clock data recovery. The circuit generally includes a clock phase adjustment circuit, receiving clock phase information and providing a clock phase adjustment signal, a clock frequency adjustment circuit, receiving clock frequency information and providing a clock frequency adjustment signal, and an adder circuit, receiving the clock phase adjustment signal and the clock frequency adjustment signal, and providing a clock recovery adjustment signal. The architectures and/or systems generally comprise those that include a clock data recovery circuit embodying one or more of the inventive concepts disclosed herein. The method generally comprises the steps of sampling the data stream at predetermined times, generating clock frequency information and clock phase information from sampled data, and altering a frequency and/or a phase of the clock signal in response to the clock frequency information and the clock phase information.

Abstract: A signal delay structure and method of reducing skew between clock and data signals in a high-speed serial communications interface includes making a global adjustment to the clock signal in the time domain to compensate for a component of the skew that is common between the clock and all data signals. This can include skew caused by the variation in frequency of the input clock from a nominal value, misalignment between the phase of the clock and data generated at the source of the two signals. The global adjustment is made through a delay component that is common to all of the clock signal lines for which skew with data signals is to be compensated. A second level adjustment is made that compensates for the component of the skew that is common to the clock and a subset of the data signals.

Abstract: A transmission and reception apparatus for at least one digital data signal is described. The digital data signal is characterized by two logical levels, first and second logical levels, with said second logical level higher than the first logical level. The apparatus comprises a transmitter, a receiver and a galvanically isolated interface arranged between the transmitter and the receiver; said transmitter, receiver and interface are arranged so as to form a two-level isolated digital channel and the transmitter comprises a block adapted to send a clock signal to the receiver. The receiver comprises, a circuit adapted to synchronize the receiver and the transmitter using the received clock signal and a circuit adapted to memorize information related to the synchronization in a storage element to hold the synchronization while the receiver is receiving said digital data. The transmitter block is adapted to send said digital data signal after the synchronization of the receiver and transmitter.

Abstract: A programmable logic device integrated circuit (“PLD”) includes high-speed serial interface (“HSSI”) circuitry in addition to programmable logic circuitry. The HSSI circuitry includes multiple channels of nominal data-handling circuitry (typically including clock and data recovery (“CDR”) circuitry), and at least one channel of nominal clock management unit (“CMU”) circuitry (typically including phase-locked loop (“PLL”) circuitry or the like). To increase the flexibility with which the channels can be used, the nominal data-handling channels are equipped to alternatively perform CMU-type functions, and the nominal CMU channel is equipped to alternatively perform data-handling functions.

Abstract: A delay means, in response to a delay control signal, performs delay control of the phase of a clock input signal, and outputs it. A selector means, during a speed test, selects a clock input signal from among a clock input signal from a delay unit, and the input signal from an external terminal. A conversion means samples the signal outputted from the selector means based on the sampling clock signal, converts a signal format and outputs it. A clock data recovery means generates a sampling clock signal having a phase depending on the signal inputted to the conversion means, and supplies it to the conversion means. By monitoring the control code for controlling the phase of the sampling clock, a correlation is obtained between a delay variation amount and a code variation amount, and a speed test is performed.

Abstract: A phase locked loop device includes a phase detector that measures a difference in phase between a reference clock signal and an output clock signal provided to a device module. The phase detector provides a pulse having a width indicative of the phase difference. If the phase difference exceeds one of a plurality of threshold values, in indicator can be asserted. Based on the indicator, a control module can take remedial action, such as providing a different clock signal to the device module or triggering an interrupt at a processor device.

Abstract: A method and apparatus are disclosed for generating phase controlled data, based on a roaming tap interpolator. The present invention recognizes that roaming tap interpolators have inherent nonlinearities and discontinuities at the boundaries of each interpolation region. A roaming tap interpolator is disclosed that shifts the interpolation curve in time in order to avoid the undesired artifacts in the interpolation curve. A roaming tap interpolator generally comprises a plurality of delay elements that delays a first signal to generate a plurality of interpolation regions each having an associated phase; a multiplexer to select one or more of the interpolation regions; and an interpolator to process the selected one or more of the interpolation regions to generate a second signal.

Abstract: Disclosed are a digital phase-frequency detector and a method of operating a digital phase-frequency detector. The detector includes an input circuit, an output circuit and a reset circuit. In use, the input circuit receives first and second input signals during a plurality of cycles, and during a given one of the cycles, generates a first intermediate signal or a second intermediate signal depending on which of the first and second input signals was received first during that given one of said cycles. The output circuit receives these intermediate signals, and outputs, during said one cycle, a first output signal or a second output signal depending on which one of intermediate signals was received by the output circuit during said one cycle. The reset circuit applies a reset signal to the input circuit under defined conditions to begin a new one of said plurality of cycles.

Abstract: There is provided a receiver comprising: a control unit for controlling the functions of the receiver; a receiving unit for receiving data signals and timing signals; and a digitally controlled delay line unit connected to the receiving unit and to the control unit. The control unit is configured to measure several samples of the received data signal and the timing signal, to determine average values of the several measured samples of the data signal and the timing signal for defining compensation values, and the digitally controlled delay line unit is configured to adjust the number of unit delay elements for compensating for skew between the data signal and the timing signal on the basis of the defined compensation values.

Abstract: A comparator compares the voltage of an envelope signal by applying envelope detection to a signal amplitude-modulated by a digital signal encoded by a Manchester code with the terminal voltage of a capacitor constituting a filter for converting the output current of a charge pump into a voltage. The charge pump charges/discharges the capacitor by discharging or charging current, according to the result of the comparison.

Abstract: An apparatus is provided to reduce transient current swings during mode transitions. Traditionally, transient supply voltage fluctuations on a chip account for a large portion of the power supply. The number of series inductances and resistances are typically minimized, while adding large decoupling capacitances between the supply voltage and ground. However, situations may arise where reduction of series inductances and resistances cannot be accomplished. Therefore, to assist in controlling the transient current swings, reduction of clocking frequencies are performed in a controlled manner.

Abstract: A unit timing signal synchronized with a high-order transmission frame is used for measuring a difference between the number of data pieces of a client signal mapped to the high-frequency frame and the number of data pieces of the output client signal by integrating the difference therebetween for each unit timing signal. Then stuffing and de-stuffing operations are performed so that a integration result is zero.

Abstract: A digital audio processing system and method is disclosed. In an embodiment, the digital audio processing system can include a phase detector to sample an input signal and provide an output to adjust a decimation rate of an input signal. In another embodiment, the digital audio processing system can include symbol recognition logic to determine a symbol using a difference between a nearest predetermined phase value to a sample and a nearest predetermined phase value to a prior sample.

Abstract: A system and method for performing output clock phase smoothing. A phase smoothing circuit is described and includes a numerically-controlled oscillator (NCO) configured to produce a plurality of NCO clock pulses at a selectable frequency that is based on an input clock. Edges of the plurality of NCO clock pulses are aligned to edges of the input clock. A phase error calculation module is coupled to the NCO and is configured to generate a corresponding phase error for each of the plurality of NCO clock pulses. A clock phase selectable delay is coupled to the phase error calculation module and is configured to adjust each of the plurality of NCO clock pulses according to the corresponding phase error to generate an output clock at the selectable frequency that are phase-adjusted to more closely match an ideal output clock phase. Edges of the output clock need not necessarily align to the edges of the input clock.

Abstract: A digital control loop and a method for clock generation. A control loop includes at least one phase detector configured to detect a phase shift of a feedback signal relative to a reference clock signal and output a correction signal on the basis of the phase shift detected. At least one control loop filter is configured to output, on the basis of the correction signal, a first control signal and a second control signal, the first control signal being substantially the same as the second control signal except that oscillations are suppressed in the second control signal. At least one first phase generator is configured to output a first clock signal on the basis of the first control signal and the first phase reference signal, wherein the first clock signal is transmitted at least partially as feedback signal to the phase detector.

Abstract: A programmable logic device (“PLD”) or the like has a plurality of data transmitter channels. Certain circuitry is shared by the channels. The shared circuitry includes at least one phase-locked loop (“PLL”) circuit for producing a primary clock signal, and global frequency divider circuitry for producing at least one global secondary clock signal based on the primary signal. The primary and global secondary signal(s) are distributed to the channels. Each of the channels includes local frequency divider circuitry for producing at least one local secondary clock signal based on the primary signal. Each channel also includes selection circuitry for selecting either the global or local secondary signal(s) for use by clock utilization circuitry of the channel. The clock utilization circuitry may include serializer circuitry for converting data from parallel to serial form.

Abstract: A novel method and apparatus for defining process variation in a digital RF processor (DRP). The invention is well suited for use in highly integrated system on a chip (SoC) radio solutions that incorporate a very large amount of digital logic circuitry. The method and apparatus provide direct measurement of fabrication process variation in circuits without requiring any additional test equipment by utilizing a time to digital converter (TDC) circuit already present in the chip. The TDC circuit relies on the time delay in an inverter chain to sample a high speed CKV clock using a slow FREF clock. Calculation of inverse time provides a direct correlation for fabrication process variation in each die.

Abstract: A Phase Locked Loop (1) used in a data and clock recovery comprising a frequency detector (10) including a quadricorrelator (2), the quadricorrelator (2) comprising a frequency detector including double edge clocked bi-stable circuits (21, 22, 23, 24) coupled to a first multiplexer (31) and to a second multiplexer (32) being controlled by a signal having a same bitrate as the incoming signal (D), and a phase detector (DFF) controlled by a first signal pair (PQ, PQ provided by the first multiplexer (31) and by a second signal pair (PI, PI) provided by the second multiplexer (32).

Abstract: A digital waveform synthesiser (1) is implemented as a single chip integrated circuit on a single chip (2) and comprises a direct digital synthesiser (10) which produces a synthesised output signal waveform on an output terminal (4) which is substantially phase and frequency locked to the phase and frequency of an externally generated input signal applied to an input terminal (5).

Abstract: A method and an improved apparatus for clock recovery from data streams containing embedded reference clock values controlled clock source includes of a controllable digital fractional divider receiving a control value from digital comparator and a clock input from a digital clock synthesizer driven by a fixed oscillator.

Abstract: A novel mechanism that is operative to observe and compare the differentiated phase of the reference and variable PLL loop signals using a frequency detector. The resultant phase differentiated error is then accumulated to yield the phase error. The operation of the loop with the frequency detector is mathematically equivalent to that of the phase detector. A frequency error accumulator is used to generate the integral of the frequency error. The frequency error accumulator also enables stopping the accumulation of the frequency upon detection of a sufficiently large perturbation, effectively freezing the operation of the loop as subsequent frequency error updates are not accumulated. Upon removal of the phase freeze event, accumulation of the frequency error and consequently normal loop operation resumes.

Abstract: The invention discloses a signal detection apparatus and method thereof for detecting whether an input signal of a set of serial ATA signals is an out of band (OOB) signal. The signal detection apparatus includes a calibrated clock generation device, a signal processor, and a logic determination device. The calibrated clock generation device generates a sampling clock signal according to a predetermined clock signal. The signal processor generates a plurality of detection results based on the sampling clock signal and the input signal. The logic determination device receives the plural of detection results and determines whether the input signal is the OOB signal.

Abstract: An apparatus and method for correcting a CPE in a signal reception apparatus of a multi-carrier communication system are provided, in which an auto-correlation of a reference signal estimated from a reference symbol among a plurality of symbols is detected, a cross-correlation between a channel estimate of the reference signal and an actual received reference signal is detected, and the CPE of the remaining symbols except the reference symbol is corrected using the auto-correlation and the cross-correlation.

Abstract: A multi-mode PLL frequency synthesizer of a wireless multi-mode transceiver is provided which includes a reference frequency source providing an oscillator signal with a constant reference frequency, a first frequency synthesizer subunit for converting the signal into carrier signals with frequencies in the range of a first frequency band, a second frequency synthesizer subunit for transforming the oscillator signal into carrier signals having frequencies in the range of a second frequency band, and a third frequency synthesizer subunit for converting the oscillator signal into an auxiliary signal with a fixed frequency. The auxiliary signal is used together with the carrier signals of the second frequency band to generate carrier signals with frequencies in the range of a third and fourth frequency band.

Abstract: A phase-locked loop includes a sample selector configured to select a set of samples from an oversampled portion of a data signal, a dynamic phase decision control configured to indicate whether a predetermined number of edges is present in the set of samples, and a phase detector configured to determine a skew condition and a direction of the skew condition of the set of samples based on the indication of the dynamic phase decision control. The phase detector is configured to determine a skew condition based on a relation between a threshold and a number of skew errors detected in the set of samples. A value of the threshold is selected according to the indication of the dynamic phase decision control. A lower value of the threshold is selected according to an indication of the dynamic phase decision control that only one edge is present in the set of samples.

Abstract: A phase detector includes a first clock driver comprising a first LC tank. The first clock driver provides a strobe to a plurality of flip-flops associated with sampled data being received by the phase detector. The second clock driver includes a second LC tank. The second clock driver provides a strobe to a plurality of flip-flops associated with sampling the phase error of the phase detector. The first and second LC tanks have different adjustable center frequencies and experience a programmable delay between the outputs of the first and second clock drivers so as to determine the data sampling phase of the phase detector.

Abstract: A clock generator and a data recovery circuit. The clock generator includes a voltage control oscillator (VCO) for generating a sampling clock and multi-phase clocks, a multiplexer for receiving the multi-phase clocks and selecting one of the multi-phase clocks to generate a selected clock according to a selection signal, a phase-frequency detector for receiving the selected clock and a reference clock and generating a phase-frequency error signal, a charge pump and loop filter for receiving the phase-frequency error signal and generating a control voltage, a phase detector for receiving the sampling clock and an input signal and generating a phase error signal, and a digital low-pass filter for receiving the phase error signal and generating the selection signal. The digital low-pass filter clears an accumulated phase error when it generates the selection signal to force the multiplexer to change the phase.

Abstract: A dual reference input receiver, and a method of receiving, wherein the input receiver includes a first input buffer which is synchronized with and enabled by a clock signal, senses a difference between the input data signal and a first reference voltage, and amplifies the sensing result; a second input buffer which is synchronized with and enabled by the clock signal, senses a difference between a second reference voltage and the input data signal, and amplifies the sensing result; and a phase detector which detects a difference between a phase of output signals of the first and second input buffers, and outputs a signal corresponding to the detection result. The first and second reference voltages may respectively be higher and lower than a median voltage of the input data signal. Thus, a single input data signal is advantageously used and a wide input data eye is provided.

Abstract: A timing recovery circuit capable of enhancing the reliability of timing recovery in a receiver apparatus in a communication system that employs the scheme of modulating the amplitude of a carrier wave.

Abstract: In one embodiment, a phase error signal generated by a phase detector is equalized to compensate for the distortion in the phase error signal due to finite circuit speeds. The equalization may be based on suppressing the low frequency components of the phase error signal. For example, the amplitude of the phase error signal may be reduced when the amplitude of the phase error signal is not changing.

Abstract: A frequency detection circuit and a detection method thereof suitable for a clock data recovery (CDR) circuit are provided. The frequency detection circuit includes a phase detector, a first delayer, a frequency detector, and a logic circuit. The phase detector samples a data signal according to a first clock signal provided by the CDR circuit and provides a phase instruction signal according to the sampling. The first delayer delays the first clock signal to obtain a second clock signal. The frequency detector samples the data signal according to the second clock signal and provides a frequency instruction signal according to the sampling. The logic circuit generates a clock instruction signal according to the phase instruction signal and the frequency instruction signal. The CDR circuit adjusts the frequency of the first clock signal according to the status of the clock instruction signal.

Abstract: Deskewing method and apparatus, including: an up/down detection unit samples a received data signal and determines in which of first through third areas of the data signal the logic level of the data signal transitions by using the result of the sampling, a lower limit detection unit detects a lower limit of the first area if the logic level of the data signal transitions in the first area, an upper limit detection unit detects an upper limit of the third area if the logic level of the data signal transitions in the third area, a phase detection unit determines a delay amount according to the upper limit detected by the upper limit detection unit and the lower limit detected by the lower limit detection unit, a buffer unit delays the data signal by the delay amount determined by the phase detection unit.

Abstract: The disclosed embodiments relate to exploiting circuitry that exists in a typical Orthogonal Frequency Division Multiplexing (OFDM) receiver to find the phase of a complex number corresponding to an input signal without implementing additional costly circuitry or employing a relatively slow inverse tangent look-up table. The magnitude of the complex number is normalized and processed through a closed loop to produce an output proportional to the phase of the complex number.

Abstract: A phase detector is described, comprising a pair of output-latched half-transparent (OLHT) module each receiving two input terminals with an inverse connection relationship with respect to two input signals as compared to each other, wherein each OLHT module of the pair comprises two stages of logic operation unit connected in series and a latch circuit electrically connected to a latter one of the two stages of logic operation unit and latching and output an output signal.

Abstract: Methods and apparatus are provided for digital compensation of clock timing errors in a VCDL. Clock timing errors in a clock and data recovery system having a voltage controlled delay loop comprised of a plurality of delay elements are compensated for by evaluating a phase of data recovered from an input signal; generating one or more uncompensated clock phase adjustment values based on the phase evaluation; generating one or more compensation terms that compensate for a non-ideal delay for one or more of the delay elements; and determining an adjustment to one or more clock phases produced by the voltage controlled delay loop based on the uncompensated clock phase adjustment values and the one or more compensation terms. The one or more compensation terms can be subtracted from the uncompensated clock phase adjustment values to generate the adjustment to the one or more clock phases.

Abstract: An apparatus comprising a first multiplexer circuit (MUX) to receive a plurality of clock phase signals at a corresponding plurality of MUX inputs and to output a first clock signal and a second clock signal that are out of phase with each other, a phase delay circuit to receive the output of the first MUX and to generate adjusted first and second clock signals that have reduced phase error with respect to detected edges of incoming data, an output MUX to receive the adjusted first and second clock signals and to output a recovered clock signal, and a control circuit coupled to output MUX select inputs. The control circuit includes logic circuitry to select the first adjusted clock signal as the recovered clock signal and to select the second adjusted clock signal as the recovered clock signal when the first adjusted clock signal nears a phase limit due to drift of the detected data edges. Other devices and methods are disclosed.

Abstract: Techniques are disclosed for detecting a packet. One technique includes sampling a received signal to produce a sequence of samples wherein the sequence of samples includes a plurality of subsequences of samples; cross correlating the subsequences of samples with a known form of the subsequence to produce cross correlations; self correlating the cross correlations to produce a plurality of self correlations; summing the self correlations; and processing the sum of the self correlations.

Abstract: A clock and data recovery apparatus reduces current consumption and enables easy integration. The inventive apparatus includes a first loop including a frequency/phase detection unit, a first charge pump unit, a multiplexing unit, a filtering unit, and a voltage controlled oscillator unit operating at a speed ¼ as fast as that of received data; a second loop having a phase detection unit operating at a speed ¼ as fast as a speed of received data, a second charge pump unit suitable for the phase detection unit, the multiplexing unit, the filtering unit, and the voltage controlled oscillator unit; a frequency lock detection unit for judging whether a frequency of a feedback clock signal falls within a desired frequency range; and a data recovery unit for recovering data from received data.

Abstract: Embodiments of the invention consist in a method of carrier synchronization, comprising determining a frequency offset estimate from a rate of change of a phase difference between a local oscillator signal and a carrier signal of a received signal; and adjusting a frequency of the local oscillator signal by the frequency offset estimate.

Abstract: A numerically-controlled phase-lock loop with input clock dependent ratio adjustment provides for narrower-bandwidth loops that lock to a wide range of frequencies and/or operation with an absent or degraded input timing reference. A timing reference characteristic detector determines an input frequency range of the input timing reference signal, the data type of the timing reference, and/or whether a timing reference signal of sufficient quality is present. A numerically controlled oscillator is controlled by a numeric ratio that is adjusted to provide the desired clock frequency output in conformity with the detected frequency range and/or data type. If the timing reference signal is absent or degraded, then the numeric ratio can be set to a fixed value or a local timing reference can be applied in order to generate the desired clock output frequency.

Abstract: A device and a method for processing high data rate serial data includes a VCO initial frequency calibration circuit. The circuit includes a frequency detection block for indicating a difference between a reference clock and a divided VCO clock, a frequency calibration block that produces a digital output signal based upon the difference between the reference clock and the divided VCO clock, and a digital-to-analog converter for producing an analog VCO adjust signal. The frequency detection block produces a plurality of signals based upon the reference clock and the divided VCO clock. A plurality of user selected inputs selects a frequency detection lock range and hysteresis range and a coarse loop open calibration lock and hysteresis range. The frequency calibration block implements a state machine for producing the digital output signal that sets the initial operating frequency then adjusts the frequency of the VCO clock.

Abstract: The present invention relates to a multiband PLL arrangement comprising a single loop PLL with a phase/frequency detecting means (1), a loop filter means (2) and a Voltage Controlled Oscillator (VCO) (3), to which PLL a reference voltage signal (Vref) is input. It further comprises a control circuit for appropriately locking the VCO (3) to the correct frequency band, said control circuit comprising a multi-window circuit (4) with at least first and second window amplitudes each defined by respective upper and lower voltage levels, and comparing means (5A, 5B) are provided for comparing a first VCO control voltage output from the loop filter means (2) with the upper and lower voltage levels of a first, broadest amplitude window.