Abstract: Disclosed herein is a temperature compensated crystal oscillator, TCXO, comprising: a crystal oscillator arrangement configured to generate an output signal of the temperature compensated crystal oscillator; and a temperature sensor arranged to generate a temperature sensor signal, wherein the output signal of the crystal oscillator arrangement is controlled in dependence on the temperature sensor signal; wherein: the temperature sensor comprises a plurality of transistor circuits; each transistor circuit comprises a transistor and a bias circuit; each transistor circuit is arranged to output a temperature signal that is dependent on the temperature of the transistor comprised by the transistor circuit; each bias circuit is configured such that the noise level in each output temperature signal is low; and the plurality of transistor circuits are arranged so that the temperature sensor signal is dependent on each of the plurality of output temperature signals.

Abstract: Disclosed is an integrated circuit amplifier for use in a crystal oscillator. The circuit amplifier comprises a transistor; a voltage dependent capacitance circuit; and a node. The voltage dependent capacitance circuit comprises a device with a voltage dependent capacitance and a bias circuit. The node is connected to a terminal of the transistor and the integrated circuit amplifier is configured such that an intrinsic capacitance of the transistor is dependent on the mean voltage at the node. The node is connected to a terminal of the voltage dependent capacitance circuit and the integrated circuit amplifier is configured such that an effective capacitance of the node is dependent on the intrinsic capacitance of the transistor and the voltage dependent capacitance of said device. When in use, the voltage dependent capacitance circuit reduces the amount of change of the effective capacitance of the node when the mean voltage at the node changes.

Abstract: Temperature compensated oscillators are provided. The oscillator comprises an oscillator circuit and a temperature compensation module. The temperature compensation module reduces temperature induced errors in the frequency of oscillation of the oscillator by providing a temperature compensation signal to the oscillator circuit based on a temperature sensor output. The temperature compensation module comprises a low pass filter configured to reduce noise in the temperature compensation signal. The low pass filter is such that, using Laplace representations of transfer functions, the transfer function H(s) of the filter is equivalent to the transfer function of a closed loop configuration in which a module having an open loop transfer function G(s) is configured to generate an output from the closed loop configuration by applying the open loop transfer function G(s) to an error between an input to the closed loop configuration and the output from the closed loop configuration.