A crystal driver integrated circuit with external oscillation signal amplitude control including an amplifier core, an input pin and an output pin, an adjustable capacitor, and a controller. The controller operates the amplifier core in any one of multiple operating modes including an oscillator mode and a bypass mode. During the bypass mode, the controller disables the amplifier core and adjusts the adjustable capacitor so that an amplitude of an oscillation signal received via the input pin from an external oscillator has a target amplitude. The external oscillation signal may be capacitively coupled for capacitive voltage division or directly coupled for impedance attenuation. An available voltage may be provided as a source voltage to the external oscillator via the output pin. An internal voltage regulator and/or switch may be included to re-provision the output pin to provide the source voltage during the bypass mode.

Provided is a method for controlling the bias current, I.sub.PIERCE, of an oscillator. The method includes acquiring or determining a digital representation encoding a bias current. The method also includes carrying out an algorithm to update the digital representation if the oscillation amplitude is measured, by one or more peak detectors, to be outside of upper and lower thresholds. Also provided is an apparatus arranged to control the bias current of an oscillator using this method, the apparatus including one or more peak detectors and a current digital to analogue converter.

A voltage system and a method of operating a voltage system are provided. The voltage system includes an oscillator and a pump device. The oscillator is configured to provide an oscillation signal exhibiting a first frequency when a voltage level of a supply voltage is greater than a reference voltage level, and to provide the oscillation signal exhibiting a second frequency greater than the first frequency when the voltage level of the supply voltage is less than the reference voltage level. The pump device is configured to provide the supply voltage, based on a frequency of the oscillation signal provided by the oscillator, by performing a charging operation.

A trigger, includes: a first voltage input terminal; a bias voltage input terminal; a first bias transistor having a scaling of N to a first component of an external device; a comparator transistor having a scaling of N to a second component of the external device; a first switch transistor and a second switch transistor; a shunt transistor having a control terminal connected to the first voltage input terminal, a second terminal connected to the second terminal of the second switch transistor, and a first terminal connected to the first terminal of the comparator transistor. The shunt transistor has an enlarging scale of M to the comparator transistor. A voltage output terminal is respectively connected to the second terminal of the first switch transistor, the control terminal of the second switch transistor, and the second terminal of the comparator transistor.

Provided is a method for controlling the bias current, I.sub.PIERCE, of an oscillator. The method includes acquiring or determining a digital representation encoding a bias current. The method also includes carrying out an algorithm to update the digital representation if the oscillation amplitude is measured, by one or more peak detectors, to be outside of upper and lower thresholds. Also provided is an apparatus arranged to control the bias current of an oscillator using this method, the apparatus including one or more peak detectors and a current digital to analogue converter.

An oscillator circuit for a signal transmitter, the oscillator circuit including: a resonant circuit (12) including a resonant inductor (LR) and a resonant capacitor (CR) parallel to the resonant inductor (LR); a driving branch (14) including a pump driver bank (38) connected to the resonant circuit (12); a feedback branch (15) connected to the resonant circuit (12), and an amplitude regulation loop (28) connected to the resonant circuit (12) via the feedback branch (15) and operable to control the pump driver bank (38). The amplitude regulation loop (28) includes: an envelope detector (30) connected to the resonant circuit (12) via the feedback branch (15), a differential amplifier (32) connected to the feedback branch (15) via the envelope detector (30), and an analog to digital converter (ADC) (34) connected to an output of the differential amplifier (32) and operable to control the pump driver bank (38).