Importance

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Abstract

A CMOS low frequency oscillator circuit comprising an amplifier (10) and an interface for connecting a first and a second terminal of an external crystal oscillator (14) in a feedback path of the amplifier (10). In one aspect, the oscillator circuit further comprises a regulated current source (24) supplying a regulated current to the amplifier (10) controlled by the voltage swing across the external crystal oscillator (14); and a constant current source (32) supplying a minimum constant current to the amplifier (10) independent of the voltage swing across the external crystal oscillator (14). In another aspect, the oscillator circuit further comprises an output stage (34) for converting an analog oscillator signal provided at the first and second terminals of the external crystal oscillator into a digital clock signal; wherein the output stage has a differential input (36) and a single-ended output (38) and includes a comparator (40) coupled with its differential input to the two terminals of the external crystal (14), the comparator (40) having a single-ended output; two parallel branches (42, 44) of series-connected inverters (42a, 42b, 42c, 44a, 44b, 44c), each branch having an input connected to the output of the comparator (40); a dynamic inverter (46) with complementary inputs each connected to a different output of the two parallel circuit branches (42, 44); and a plurality of series-connected output inverters (48, 50, 52).

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First Claim