Crystal oscillator temperature compensating circuit

Claim 1

A temperature compensating circuit for an oscillator having a frequency determining crystal, and a voltage variable reactance coupled to the crystal for varying the oscillator frequency in response to a control voltage applied to said reactance, comprising: first current generating means for independently creating a substantially linear current versus temperature variation in a middle temperature range and a non-linear variation in both a hot and a cold temperature range; second current generating means for creating a substantially non-linear current versus temperature variation in said cold temperature range, said second current generating means including circuitry for independently determining the operative temperature range of said second current generating circuit; third current generating means for creating a substantially non-linear current versus temperature variations in said hot temperature range, said third current generating means including circuitry for independently determining the operative temperature range of said third current generating circuit; first current mirror means, coupled to the first current generating means and the third current generating means, for summing currents of said first and third current generating means to produce a first current sum; second current mirror means, coupled to the first current generating means and the second current generating means, for summing currents of said first and second current generating means to produce a second current sum; means for summing the currents of said first and second current mirror means to produce a total current sum, and for generating a control voltage with the same temperature variation as said total current sum; and means for coupling said control voltage to said reactance means whereby said oscillator frequency is maintained at a substantially constant value over all of said temperature ranges.