TEMPERATURE CORRECTING CIRCUIT OF NARROW BAND PASS FILTER BY CRYSTAL FILTER

摘要

PURPOSE: To maintain an output level, a band width characteristic and passing band width, which follow a temperature variation so as to be constant by controlling a tuning frequency of the crystal filter by reading out correction data from a temperature correction table derived in advance in accordance with an ambient temperature. ;CONSTITUTION: Set values of the corresponding D/A converters 13, 23 extending over all working temperatures at every crystal filter and written in a temperature correction table 20. A deviation of a tuning frequency of each crystal filter 14, 24, which follows a variation of an ambient temperature is corrected by a control voltage applied to variable capacity diodes 12, 22. This control voltage is supplied from the D/A converters 13, 23, and a correction value corresponding to the ambient temperature is read out of the table 20 and set. A correction temperature is inputted from a temperature sensor 18 and used as a temperature parameter at the time of referring to the temperature correction table 20 by a control part 19. Fine adjustment of the tuning frequency of the filter 14 is executed by varying a series capacity value of the variable capacity diode 12 connected to the filter 14.;COPYRIGHT: (C)1995,JPO