Temperature-compensated crystal oscillator (TCXO) is a quartz crystal oscillator in which the change in oscillation frequency generated by the change in ambient temperature is reduced by an additional temperature compensation circuit.In the TCXO, there are two types of compensation methods for the temperature drift of the quartz crystal oscillator frequency, namely, the direct compensation and the indirect compensation: (1) direct compensation type The direct compensation type TCXO consists of a temperature compensation circuit composed of a thermistor and a resistive element connected in series with the quartz crystal oscillator.
(1) Direct compensation type
The direct compensation type TCXO is a temperature compensation circuit composed of a thermistor and a resistive element, which is connected in series with the quartz crystal oscillator in the oscillator. When the temperature changes, the resistance of the thermistor and the equivalent series capacitance of the crystal change accordingly, thus offsetting or reducing the temperature drift of the oscillation frequency. This compensation method has simple circuit, low cost, saves printed circuit board (PCB) size and space, and is suitable for small and low-voltage small-current occasions. However, when the crystal oscillator accuracy is required to be less than ±1pmm, the direct compensation method is not suitable.
(2) Indirect compensation type
The indirect compensation type is divided into analog and digital two types. The analog indirect temperature compensation uses temperature sensing elements such as thermistors to form a temperature-voltage conversion circuit and applies the voltage to a varactor diode connected in series with the crystal oscillator to compensate for the nonlinear frequency drift of the crystal oscillator through the change of the series capacitance of the crystal oscillator. This compensation method achieves a high accuracy of ±0.5ppm, but is limited at low voltages of 3V or less. Digital Indirect Temperature Compensation is to convert analog quantities into digital quantities by adding a stage of analog/digital (A/D) converter after the temperature-voltage converter circuit in the analog-type compensation circuit. This method can realize automatic temperature compensation and make the crystal oscillator frequency stability very high, but the specific compensation circuit is more complicated and costly, and it is only applicable to base stations and broadcasting stations, etc., which require high precision.
TCXO development status: TCXO has been greatly developed in the last decade or so, including in the research, development and production of precision TCXO. In the late 70's car phone with TCXO volume of more than 20, the current mainstream products down to 0.4, ultra-miniaturized TCXO device volume is only 0.27. In 30 years, the volume of the TCXO shrinks to 1/50 or even 1/100. the current high stability of the TCXO device, the accuracy can be up to ± 0.05 ppm. high-precision, low-power and miniaturization is still the TCXO research issues. TCXO research topics. In the miniaturization and chip, faced with a number of difficulties, of which there are two main points: First, miniaturization will make the quartz crystal oscillator frequency variable amplitude becomes smaller, the temperature compensation is more difficult; Second, the chip package in its reflow soldering operations, due to the soldering temperature is much higher than the maximum permissible temperature of the TCXO, the crystal oscillator will make the frequency change, if not to adopt the limit of the local heat dissipation cooling measures, it is difficult to will be Without local heat dissipation and cooling measures, it is difficult to control the frequency change of TCXO below ±0.5×10-6. However, the improvement of the technical level of TCXO has not reached the limit, and the content and potential of innovation are still large.
Applications of TCXO
The development of quartz crystal oscillator and its application in wireless system, due to the TCXO has a high frequency stability, and small size, in the small current can be started quickly, its application field focuses on expanding to the mobile communication system.TCXO as a reference oscillator for the sending channel to provide a frequency reference, and at the same time as the receiving channel as the first stage of the native oscillator; another TCXO as the 2nd stage of the The other TCXO acts as the 2nd level local oscillator and inputs its oscillating signal to the 2nd frequency converter. Currently, the frequency stability required by cell phones is 0.1~2.5ppm (-30~+75℃), but for cost considerations, the specification usually chosen is 1.5~2.5ppm.
Application: Test Equipment Frequency Range: 1MHz-160MHz
Frequency:45 5.12 6 6.4 8.192 9.216 10 10.24 12 12.8 13 14.4 15.36 16.38 16.384 19.44 19.68 19.8 20 30.72 32.768 36.864 38.88 40 52 50 77.76 80 100 155.52