Folding type A/D converter and folding type A/D converter circuit

An A/D conversion circuit for converting an external analog input signal inputted from the outside into digital form to output an external digital output voltage to the outside,

• said A/D conversion circuit comprising:
• a reference-voltage supply portion outputting a first number of reference voltages selected at first voltage intervals in a first period, and in a second period, supplying a second number of reference voltages selected at second voltage intervals shorter than said first voltage intervals, on the basis of an A/D-conversion control signal;
• a sub-A/D converter converting said first number of reference voltages from analog to digital in said first period to output an upper partial digital output voltage as well as to output said A/D-conversion control signal related to a A/D-conversion result, and converting said second number of reference voltages from analog to digital in said second period to output a lower partial digital output voltage;
• and
• a digital-output-voltage output portion combining said upper and said lower partial digital output voltages to output said external digital output voltage,
• said sub-A/D converter comprising:
• a first amplifier portion receiving and amplifying said analog input voltage and a plurality of reference voltages;
• an input-voltage conversion portion receiving said analog input voltage and said plurality of reference voltages which are amplified in said first amplifier portion, and converting said analog input signal on the basis of said plurality of reference voltages to output a plurality of conversion voltages;
• a least-significant-bit data output portion outputting a first partial digital output voltage having a first bit count on the basis of a comparison result between each of said plurality of conversion voltages and a fixed value;
• a second amplifier portion receiving and amplifying said analog input voltage and a predetermined number of reference voltages extracted from said plurality of reference voltages;
• and
• a most-significant-bit data output portion outputting a second partial digital output voltage having a second bit count on the basis of a comparison result between said analog input voltage and each of said predetermined number of reference voltages which are amplified in said second amplifier portion,
• wherein said digital output voltage consists of said second partial digital output voltage as a most-significant-bit group and said first partial digital output voltage as a least-significant-bit group;
• wherein each of said first and said second amplifier portions has an amplification factor that varies according to a control signal;
• said sub-A/D converter, in said first period, receiving said external analog input voltage and said first number of reference voltages as said analog input voltage and said plurality of reference voltages, respectively, while setting each amplification factor of said first and said second amplifier portions to be a first amplification factor according to said control signal, and outputting said digital output voltage as said upper partial digital output voltage;
• and
• said sub-A/D converter, in said second period, receiving said external analog input voltage and said second number of reference voltages as said analog input voltage and said plurality of reference voltages, respectively, while setting each amplification factor of said first and said second amplifier portions to be a second amplification factor larger than said first amplification factor according to said control signal, and outputting said digital output voltage as said lower partial digital output voltage.