A temperature compensated crystal oscillator , comprising: a crystal oscillator, a primary temperature compensation signal generator arranged to produce a primary temperature compensation signal which effects a primary temperature compensation action over an entire temperature compensation temperature range of the temperature compensated crystal oscillator, which action is complementary, over said entire temperature compensation temperature range, to a frequency versus temperature characteristic of the crystal oscillator, to reduce a frequency versus temperature error of the crystal oscillator, leaving a residual frequency versus temperature error, and a secondary temperature compensation signal generator arranged to produce a secondary temperature compensation signal which effects a secondary temperature compensation action within said temperature compensation temperature range, which action is complementary to said residual frequency versus temperature error, to reduce said residual frequency versus temperature error, wherein; the residual frequency versus temperature error of the temperature compensated crystal oscillator is configured to be characterized, and the secondary temperature compensation signal generator comprises an analog circuit arranged to generate at least one analog temperature compensation signal as a function of an analog temperature sensor output signal , said function comprising a plateau region, and a continuously and smoothly connected substantially higher slope region, and any one or more of a horizontal position of the substantially higher slope region, a slope value in the substantially higher slope region, and a function value change magnitude over the substantially higher slope region are adjustable. a primary temperature compensation signal generator arranged to produce a primary temperature compensation signal which effects a primary temperature compensation action over an entire temperature compensation temperature range of the temperature compensated crystal oscillator, which action is complementary, over said entire temperature compensation temperature range, to a frequency versus temperature characteristic of the crystal oscillator, to reduce a frequency versus temperature error of the crystal oscillator, leaving a residual frequency versus temperature error, and a secondary temperature compensation signal generator arranged to produce a secondary temperature compensation signal which effects a secondary temperature compensation action within said temperature compensation temperature range, which action is complementary to said residual frequency versus temperature error, to reduce said residual frequency versus temperature error, wherein; the residual frequency versus temperature error of the temperature compensated crystal oscillator is configured to be characterized, and the secondary temperature compensation signal generator comprises an analog circuit arranged to generate at least one analog temperature compensation signal as a function of an analog temperature sensor output signal , said function comprising a plateau region, and a continuously and smoothly connected substantially higher slope region, and any one or more of a horizontal position of the substantially higher slope region, a slope value in the substantially higher slope region, and a function value change magnitude over the substantially higher slope region are adjustable. <EOS>