Series-parallel A-D converter

A series-parallel A-D converter comprising

• an input terminal receiving a sample signal to be A-D converted,
• a high potential point,
• a low potential point,
• a plurality of resistor groups connected in series between said high potential point and said low potential point for dividing a potential difference between said high potential point and said low potential point to provide a plurality of first reference potentials including potentials at said high and low potential points and put in a first descending order,
• said first reference potentials paired adjacent to each other in said first order defining upper and lower limits of a plurality of voltage zones corresponding to said resistor groups,
• each of said resistor groups including a plurality of resistors connected in series for dividing a potential difference between the upper and lower limits of said corresponding voltage zone to provide a plurality of second reference potentials including said first reference potentials and put in a second descending order,
• said second reference potentials forming a reference potential band for each of said voltage zones corresponding thereto,
• a plurality of bus line groups each having a plurality of analog bus lines arranged in a third order,
• a plurality of potential line bands provided in one-to-one corresponding relation to said reference potential bands and each including a plurality of reference potential lines, said second reference potential in the corresponding reference potential band being applied respectively to said reference potential lines in said second order,
• first A-D conversion means for comparing said sample signal with said first reference potentials to provide a first conversion result specifying as a corresponding zone one specific voltage zone having said upper and lower limits between which said sample signal falls,
• a plurality of switch groups provided in corresponding relation to said voltage zones, and
• second A-D conversion means for comparing said sample signal with said second reference potentials to provide a second conversion result specifying level relation between said sample signal and said second reference potentials,
• each of said reference potential bands including a high potential group having said second reference potentials of relatively high levels and a low potential group having said second reference potentials of relatively low levels,
• each of said potential line bands including a high potential line group and a low potential line group, said high potential group being applied to said high potential line group, said low potential group being applied to said low potential line group,
• each of said switch groups including a plurality of switches disposed on said reference potential lines and said analog bus lines for connecting said reference potential lines in the corresponding potential line band to said analog bus lines with said second and third orders associated with each other,
• said switches only in one of said switch groups corresponding to said specific voltage zone specified by said first A-D conversion means as said corresponding zone being permitted to conduct,
• said switches disposed on each of said analog bus lines being smaller in number than said reference potential bands.