Analog-digital converter

Claim 1

An apparatus for converting an analog signal into a digital signal in a selected gain mode and adapted to be arranged in the form of a single chip LSI, said apparatus comprising: first terminal means for receiving an analog signal; second terminal means for connecting an external variable gain amplifier so as to amplify said received analog signal, the gain of said amplifier being variable according to a gain select signal applied thereto; a register for storing data for determining the gain mode of said variable gain amplifier, said data being settable according to a command externally applied thereof; a successive approximation A/D converter disposed to receive an analog signal amplified by said amplifier, said converter being operative to convert said amplified signal into a digital signal whose digits are determined successively from a digit of highest order to a digit of lowest order by successive comparison of said amplified analog signal with different levels of reference signals; a mode control gate means coupled to an output of said successive approximation A/D converter and responsive to a determination by said A/D converter of the values of a predetermined number of higher order digits of the digital signal obtained during the operation of A/D conversion of the amplified analog signal by said A/D converter, said predetermined number being determined according to the mode set by said data stored in said register for producing a first signal indicative of whether the gain of said amplifier is to be changed or not depending on said determined values of the higher order digits; third terminal means for coupling said first signal externally of said apparatus so that said first signal is supplied, as said gain select signal, to said amplifier connected to said first terminal means; and said mode control gate means further producing a second signal which causes said A/D converter to continue its operation of A/D conversion of said amplified analog signal when the gain of said amplifier is not to be changed and to stop its operation of A/D conversion of said amplified analog signal when the gain of said amplifier is to be changed and again start its operation to effect the A/D conversion on the newly amplified analog signal after the gain of said amplifier has been changed according to said first signal.

Claim 2

An apparatus for converting an analog signal into a digital signal in a selected gain mode and adapted to be arranged in the form of a single chip LSI, said apparatus comprising: first terminal means for receiving an analog signal; second terminal means for connecting an external variable gain amplifier so as to amplify said received analog signal, the gain of said amplifier being variable according to a gain select signal applied thereto; a register for storing data for determining the gain mode of said variable gain amplifier, said data being settable according to a command externally applied thereof; a successive approximation A/D converter disposed to receive an analog signal amplified by said amplifier, said converter being operative to convert said amplified signal into a digital signal whose digits are determined successively from a digit of highest order to a digit of lowest order by successive comparison of said amplified analog signal with different levels of reference signals; a mode control gate means coupled to an output of said successive approximation A/D converter and responsive to a determination by said A/D converter of the values of a predetermined number of higher order digits of the digital signal obtained during the operation of A/D conversion of the amplified analog signal by said A/D converter, said predetermined number being determined according to the mode set by said data stored in said register for producing a first signal indicative of whether the gain of said amplifier is to be changed or not depending on said determined values of the higher order digits; third terminal means for coupling said first signal externally of said apparatus so that said first signal is supplied, as said gain select signal, to said amplifier connected to said first terminal means; and said mode control gate means further producing a second signal which causes said A/D converter to continue its operation of A/D conversion of said amplified analog signal when the gain of said amplifier is not to be changed and to stop its operation of A/D conversion of said amplified analog signal when the gain of said amplifier is to be changed and again start its operation to effect the A/D conversion on the newly amplified analog signal after the gain of said amplifier has been changed according to said first signal.