A method for correcting frequency errors in the local reference frequency
crystal oscillator of a GPS receiver begins with a step in which the
ordinary temperature response of a crystal is characterized. A hardware
circuit is incorporated with that crystal to mirror that same
characteristic. A temperature sensor is used to control a compensation
applied. The combination outputs a fairly flat temperature response,
e.g., near zero delta-frequency change over the operating temperature
range. But this flat response has an unknown offset from the true
frequency. A next step finds a precision timing reference, such as when
the receiver locks onto and tracks GPS satellites. The receiver then
knows time precisely and a navigation software can compute the offset
accurately. A value is stored for that offset in memory. Such value is
thereafter recalled at each cold start and is used by software to remove
the expected frequency offset.