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Oversampling A/D converter comprising an additional capacitor switched in synchronism with switchin of an input capacitor
| Details |
Inventors: Kuraishi, Yoshiaki;
Assignee: NEC Corporation (Tokyo, JP)
Primary Examiner: Shoop, Jr.; William M.
Assistant Examiner: Kim; Helen
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Besides an input switched capacitor (14) for sampling an input analog signal into output electric charges, an oversampling analog-to-digital converter comprises an additional switched capacitor (47) for sampling, into additional electric charges in synchronism with the input switched capacitor, controlled electric charges produced by a capacitor array (24) which is coupled to a reference voltage source (23) and is controlled by a predetermined number of control signals produced by a control logic (22) in response to an output digital signal. A summing circuit delivers the output and the additional electric charges to an integrator (15) connected to a quantizer (21) which produces a quantized signal substantially identical with the digital signal. Preferably, the summing circuit comprises a connecting switch (49) for supplying the output and the additional electric charges to the integrator in synchronism with the input and the additional switched capacitors. A switch array (25) is controlled by the control signals to make the capacitor array produce the controlled electric charges. |
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DETAILED DESCRIPTION It is therefore an object of the present invention to provide an oversampling analog-to-digital converter which is operable at a high oversampling frequency.
It is another object of this invention to provide an oversampling analog-to-digital converter of the type described, which comprises an integrator operable at a high speed.
It is still another object of this invention to provide an oversampling analog-to-digital converter of the type described, by which analog-to-digital conversion can precisely be carried out.
It is yet another object of this invention to provide an oversampling analog-to-digital converter of the type described, for which increased power consumption is unnecessary.
Other objects of this invention will become clear as the description proceeds.
For describing the gist of this invention it is possible to understand that an oversampling analog-to-digital converter has a converter input terminal supplied with an input analog signal and comprises an input switched capacitor connected to the input terminal for sampling the analog signal into output electric charges, an integrator for integrating input electric charges into an integrated signal, a quantizer for quantizing the integrated signal into an output digital signal, control logic responsive to the digital signal for producing a predetermined number of control signals, a reference voltage source, a capacitor array coupled to the reference voltage source and responsive to the control signals for producing controlled electric charges, and combining means connected to the input switched capacitor, the capacitor array, and the integrator for combining the output electric charges and the controlled electric charges into the input electric charges.
According to this invention, the above-described oversampling analog-to-digital converter is characterized in that the combining means comprises: (A) an additional switched capacitor connected to the capacitor array for sampling in cooperation with the capacitor array the controlled electric charges into additional electric charges in synchronism with sampling of the analog signal; and (B) summing means connected to the input switched capacitor, the additional switched capacitor, and the integrator for summing the output electric charges and the additional electric charges into the input electric charges
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