Low voltage crystal oscillator having native NMOS transistors used for coupling/decoupling to/from GPIO. The native NMOS transistors function properly at a low supply voltage when on (low resistance) and a high supply voltage when off (high resistance). Oscillator Gm driver bias resistors are repurposed to degenerate the native NMOS transistors when they are off, thereby reducing the leakage current thereof (oscillator circuit decoupled from GPIO nodes). This ensures compliance with the CMOS IIH leakage current specification during an external clock (EC) mode at a high supply voltage.

A Pierce oscillator is provided with a transconductance amplifier transistor having a DC drain voltage that is regulated to equal a reference voltage independently from a DC gate voltage for the transconductance amplifier transistor.

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.

An oscillation circuit includes an oscillator, first and second capacitors connected between two terminals of the oscillator, and an amplification circuit having an input terminal connected to a connecting point between the oscillator and the first capacitor and an output terminal connected to a connecting point between the first capacitor and the second capacitor. The amplification circuit includes a first n-type transistor and a first p-type transistor respectively having source terminals, the connecting point of which is connected to the output terminal of the amplification circuit, a second p-type transistor connected to a gate terminal of the first n-type transistor, and a second n-type transistor connected to a gate terminal of the first p-type 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.

A method and a circuit for exciting a crystal oscillation circuit are disclosed herein. The crystal oscillation circuit comprising: charging, with a charging circuit, a voltage-controlled oscillator; providing, with the voltage-controlled oscillator, an exciting signal; blocking, with a direct current blocking capacitor, direct current from the voltage-controlled oscillator to the crystal oscillation circuit; and exciting, with the exciting signal, the crystal oscillation circuit. The circuit for exciting a crystal oscillation circuit, comprising: a charging circuit; a voltage-controlled oscillator coupled to the charging circuit and configured to provide an exciting signal to the crystal oscillation circuit; and a direct current blocking capacitor connected between the voltage-controlled oscillator and the crystal oscillation circuit and configured to block direct current from the voltage-controlled oscillator.

A temperature compensated oscillator includes a resonator element, an oscillation circuit, and a temperature compensation circuit. Assuming an observation time as T, an MTIE value at 0.1 s<1 s is 1.3 ns or less, an MTIE value at 1 s<10 s is 1.3 ns or less, an MTIE value at 10 s<100 s is 1.8 ns or less, an MTIE value at 100 s<1000 s is 2.9 ns or less, a TDEV value at 0.1 s<10 s is 47 ps or less, a TDEV value at 10 s<100 s is 65 ps or less, and a TDEV value at 100 s<1000 s is 94 ps or less.

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.

A low voltage crystal oscillator (XTAL) driver with feedback controlled duty cycling for ultra low power biases an amplifier for an XTAL in the sub-threshold operating regime. A feedback control scheme can be used to bias the amplifier for an XTAL biased in the sub-threshold operating regime. The amplifier of a XTAL oscillator can be duty cycled to save power, e.g., the XTAL driver can be turned off to save power when the amplitude of the XTAL oscillation reaches a maximum value in range; but be turned back on when the amplitude of the XTAL oscillation starts to decay, to maintain the oscillation before it stops. In addition or alternatively, a feedback control scheme to duty cycle the amplifier of a XTAL oscillator can be used to monitor the amplitude of the oscillation.

A low voltage crystal oscillator (XTAL) driver with feedback controlled duty cycling for ultra low power biases an amplifier for an XTAL in the sub-threshold operating regime. A feedback control scheme can be used to bias the amplifier for an XTAL biased in the sub-threshold operating regime. The amplifier of a XTAL oscillator can be duty cycled to save power, e.g., the XTAL driver can be turned off to save power when the amplitude of the XTAL oscillation reaches a maximum value in range; but be turned back on when the amplitude of the XTAL oscillation starts to decay, to maintain the oscillation before it stops. In addition or alternatively, a feedback control scheme to duty cycle the amplifier of a XTAL oscillator can be used to monitor the amplitude of the oscillation.