Compact and high-speed judging circuit using misfets

摘要

To judge whether or not the number of high-level bits among N (N. ltoreq.2) bits of an input signal is greater than a predetermined number M (1≦M N), a judging circuit has a differential amplifier, N primary MISFETs, M secondary MISFETs, and primary and secondary resistors having the same resistance. Sources of the primary MISFETs are connected to the ground in common. Drains of the primary MISFETs are connected to one end of the primary resistor in common. The other end of the primary resistor is supplied with a power-supply voltage. Gates of the primary MISFETs are supplied with the N bits, respectively. The primary MISFETs have on-currents, respectively, which are equal to one another. An inverted input terminal of the amplifier is connected to the above- mentioned one end of the primary resistor. Sources of the secondary MISFETs are connected to the ground in common. Drains of the secondary MISFETs are connected to one end of the-secondary resistor in common. The other end of the secondary resistor is supplied with the power-supply voltage. Gates of the secondary MISFETs are supplied with a gate voltage in common so that the secondary MISFETs are constantly kept in an on- state. The secondary MISFETs have on-currents, respectively, equal to one another and equal to the on-currents of the primary MISFETs. A non- inverted input terminal of the amplifier is connected to the above- mentioned one end of the secondary resistor.