| 摘要 |
A continuous time delta-sigma modulator with a self cut off current mode DAC is provided to suppress a jitter noise by supplying a constant amount of charges to a DAC, even when a size of a coupling capacitor is varied. A DAC(Digital to Analog Converter) includes a coupler capacitor(CC), first switches, at least one current source(32,33), and second and third switches. The first switch couples both ends of the coupling capacitor with a reference voltage according to a first control signal. The current source generates a current with a constant value when a voltage difference between both ends is bigger than a predetermined level. When the voltage difference becomes smaller than the predetermined level, the current generated by the current source is decreased. The second switch selectively couples the other end of the coupling capacitor with the current source according to a second control signal and a digital output. An activation period of the second control signal is not overlapped with that of the first control signal. The third switch couples one end of the coupling capacitor with a first input terminal of the operational amplifier according to the second control signal.
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