Bias circuit for an analog-to-digital converter that works on the principle of subdivision

摘要

Through first and second external terminals (T2, T3), fixed potentials are applied to both ends of a first stage of ladder resistor network. A second stage of ladder resistor network is connected at one end to a second transistor (Q2). The first external terminal (T2) is connected to a first transistor (Q5) through a resistor (RM), the resistor (RM) and the resistors of the first and second stage of ladder resistor networks being of the same kind. A positive input terminal of an operational amplifier (1) is connected to a node (A) between the resistor (RM) and the first transistor (Q5). A negative input terminal of the amplifier (1) receiving a reference voltage is connected to the second external terminal (T3). The first and second transistors (Q2, Q5) are driven by the output signal of the amplifier (1). The amplifier (1) cooperates with the first transistor (Q5) such that a potential at the node (A) is equal to the potential of the reference voltage. As a result, a current (I2/M (M = constant)) flowing through the resistor (RM) is proportional to a current (I2) flowing through the first stage of ladder resistor network. Since the current, which is based on the operation of the second transistor (Q2), flows into the second stage of ladder resistor network, the current flowing through the first transistor (Q5) is proportional to a current (I3) flowing through the second stage of ladder resistor network.