For example, an apparatus may include a digitally-controlled frequency multiplier, which may be controllable according to a digital control input, to generate an output frequency signal having an output frequency, for example, by multiplying an input frequency of an input frequency signal. For example, the digitally-controlled frequency multiplier may include a phase generator configured to generate a plurality of phase-shifted signal groups corresponding to a respective plurality of first phase-shifts applied to the input frequency signal, a plurality of digital clock multipliers controllable according to the digital control input to generate a respective plurality of frequency-multiplied signals based on the plurality of phase-shifted signal groups, and a combiner to generate the output frequency signal based on a combination of the plurality of frequency-multiplied signals.

A hybrid Phase Locked Loop, PLL (10, 34A, 34B, 38) employs an analog control loop during a first period of operation, such as steady-state operation, to achieve a simple design, stable operation at very high frequency, and low phase noise. During a second period of operation, such as frequency changes, a digital control loop takes over. Under digital control, charge pump (14) inputs are forced to be at or near 100% duty cycle for maximum loop filter (16) charging and fast, linear frequency change. The digital control loop monitors when the target frequency is reached, and exits the second period of operation with the proper feedback signal phase. The digital control loop can operate in two control modes. In a first mode, the phase of the divided VCO output signal is synchronized with the phase of a periodic reference signal throughout the frequency change. In a second mode, the frequency and phase are controlled in separate steps, by controlling the integer and fractional parts of delta-sigma generated division number. Three embodiments are disclosed. In a first embodiment, a switch substitutes constant charge pump (14) inputs for the outputs of a phase frequency detector, PFD (12) to maximize the loop filter (16) current. In a second embodiment, one pulse of one of the periodic signals is suppressed, forcing the PFD (12) to output charge pump input signals at near 100% duty cycle. In a third embodiment, all the cycles of one of the periodic signals are suppressed, forcing PFD (12) output signals to 100% duty cycle.

Disclosed are circuits and method for reducing or eliminating reference spurs in frequency synthesizers. In some implementations, a phase-locked loop (PLL) such as a Frac-N PLL of a frequency synthesizer can include a phase frequency detector (PFD) configured to receive a reference signal and a feedback signal. The PFD can be configured to generate a first signal representative of a phase difference between the reference signal and the feedback signal. The PLL can further include a compensation circuit configured to generate a compensation signal based on the first signal. The PLL can further includes a voltage-controlled oscillator (VCO) configured to generate an output signal based on the compensation signal. The compensation signal can include at least one feature for substantially eliminating one or more reference spurs associated with the PLL.

In accordance with an embodiment, a method of operating a fractional-N phase locked loop (FN-PLL) includes: dividing a first clock signal using a multi-modulus divider (MMD) based on a modulus control signal to form a frequency-divided clock signal, where the first clock signal is based on an output clock of the PLL; generating the modulus control signal based on a divider control input value using a delta-sigma modulator (DSM); and when a fractional portion of the divider control input value is within a first range of values, and repeatedly removing a first number of clock cycles from the first clock signal before dividing the first clock signal using the MMD, where the first number of clock cycles is a non-integer number of clock cycles.

Disclosed is a pulse elimination circuit, a voltage detection circuit and a detection method, referring to a field of electronic circuit technology. The pulse elimination circuit comprises: a clock generation circuit configured to receive a logic signal and a first input signal and generate a clock signal according to the logic signal and the first input signal; a counter coupled with the clock generation circuit and configured to receive the clock signal and count a number of cycles of the clock signal to generate a second input signal; a signal output circuit coupled to the counter and configured to supply a first input signal to the clock generation circuit and generate a pulse elimination signal based on the second input signal. Therefore, in a process of voltage detection, this circuit can eliminate a false trigger caused by short pulse and improve voltage detection accuracy.

Described herein is a method and apparatus for reducing ISI in a single-bit modulator without reducing the dynamic range of the modulator. In one embodiment, the signal fed back to the input of the modulator is not the single-bit outputs of a quantizer as in the prior art, but rather patterns of such outputs. The patterns are selected so that each pattern has the same number of transition edges and there is thus no mismatch of transition times. In one embodiment, the patterns are created by digital logic. In another embodiment, an analog signal is added to the error signal in the feedback loop which causes the quantizer to generate the patterns. When the amplitude of the input signal exceeds a certain level, the modulator reverts to the typical operation of a prior art modulator, thus preserving the full dynamic range of the modulator.

Described herein is a method and apparatus for reducing ISI in a single-bit modulator without reducing the dynamic range of the modulator. In one embodiment, the signal fed back to the input of the modulator is not the single-bit outputs of a quantizer as in the prior art, but rather patterns of such outputs. The patterns are selected so that each pattern has the same number of transition edges and there is thus no mismatch of transition times. In one embodiment, the patterns are created by digital logic. In another embodiment, an analog signal is added to the error signal in the feedback loop which causes the quantizer to generate the patterns. When the amplitude of the input signal exceeds a certain level, the modulator reverts to the typical operation of a prior art modulator, thus preserving the full dynamic range of the modulator.

A timing method and a clock device are provided. The method includes: determining a timing point according to a timing duration of a clock device, where a clock period of the clock device is T, the timing duration is N times of a first time duration, and the first time duration is equal to Q.sub.2T, where Q.sub.2=Q.sub.1 or Q.sub.2=Q.sub.1, and Q.sub.1=C/T, N is a positive integer, Q.sub.1 is not an integer, and C is a constant (210); and performing one adjustment on timing time of the clock device each time P first time durations elapse, where an amount of time for each adjustment is one clock period T, P=1/|Q.sub.2Q.sub.1| (220). Based on this method, accurate timing can still be effectively implemented when a ratio of a constant C (for example, 1.25 ms) to a clock period is not an integer.

The techniques described herein relate to duty cycle error calibration. An example apparatus includes a multi-modulus divider (MMD) circuit configured to receive a first digital code corresponding to a first time delay and included in a first plurality of digital codes associated with a first range of time delays, divide a clock signal by a divisor to generate a divided clock signal, and delay the divided clock signal by the first time delay to generate a delayed clock signal. The apparatus may further include a digitally controlled delay line (DCDL) circuit configured to receive a second digital code corresponding to a second time delay and included in a second plurality of digital codes associated with a second range of time delays, and delay the delayed clock signal by the second time delay to generate a feedback clock signal to reduce a difference between the feedback and a reference clock signal.

A timing method and a clock device are provided. The method includes: determining a timing point according to a timing duration of a clock device, where a clock period of the clock device is T, the timing duration is N times of a first time duration, and the first time duration is equal to Q.sub.2T, where Q.sub.2=Q.sub.1 or Q.sub.2=Q.sub.1 and Q.sub.1=C/T, N is a positive integer, Q.sub.1 is not an integer, and C is a constant (210); and performing one adjustment on timing time of the clock device each time P first time durations elapse, where an amount of time for each adjustment is one clock period T, P=1/|Q.sub.2Q.sub.1| (220). Based on this method, accurate timing can still be effectively implemented when a ratio of a constant C (for example, 1.25 ms) to a clock period is not an integer.