1. Field of the Invention
The present invention relates to a temperature compensating device and satellite signal receiving system, and more particularly, to a temperature compensating device and satellite signal receiving system which compensates for effects of ambience temperature variation through current stabilizing, to ensure normal system operation.
2. Description of the Prior Art
Temperature is a critical factor in characteristics of electronic component; therefore, an ideal electronic product must be able to maintain a stable performance within a reasonable temperature range. To meet this requirement, electronic systems have temperature compensating mechanisms to compensate for effects of temperature changes.
In a satellite receiver, for example, after an antenna receives radio frequency signals transmitted by a satellite, a radio frequency amplifier first amplifies the received radio frequency signals, and then a mixer utilizes an oscillating signal of a local oscillator to lower the radio frequency signals to an intermediate or baseband frequency. In this process, abnormal operations in the mixer or the local oscillator would cause demodulation or decoding failure of analog or digital circuits in subsequent stages, leading to malfunction of the satellite receiver. A key influencing factor in operations of the mixer or the local oscillator is ambience temperature change, mainly because satellite receives are often situated outdoors and unsheltered; and in regions where outdoor temperature differences may exceed 50 degrees Celsius, such vast temperature ranges may cause changes in characteristics of electronic components (e.g. resistance values, capacitance values, conduction impedance of transistors, etc.), leading to malfunction of the mixer or the local oscillator.
Specifically, the mixer principally operates by utilizing a local oscillator to multiply the radio frequency signals and the local oscillating signal, and then filtering out unneeded signals with a band-pass filter. The local oscillator has a basic structure of a loop constructed from band-pass filters and amplifiers, mainly for repeatedly amplifying noise signals to acquire needed oscillations, and the band-pass filter filters signals at designed frequencies. As is well known by the industry, a multitude of electronic components, e.g. transistors, capacitors, resistors, etc, are required to implement the mixer and the local oscillator, thus making them prone to temperature differences.
Conventional temperature compensating mechanisms are usually implemented through fixed voltages, which have limited stabilizing effects on transistors, thus a fixed current temperature compensating mechanism is required.