AMPLIFIER CIRCUIT

PURPOSE:To attain amplification at a low voltage by providing a current source applying a current having a relation with a collector current of an input stage transistor (TR) to a base of an output stage TR. CONSTITUTION:The current source is formed by a current mirror circuit comprising TRs 7, 8 having equal emitter area. Then a current equal to the collector current of the input stage TR9 is fed to a base of the output stage TR10. Thus, the current amplification factor IC/IB is nearly equal to the product of the current amplification factor of the Darlington circuit. Since the operating voltage is a base-emitter forward voltage drop VBE9, the amplification at a low voltage is attained. In replacing the TRs 7, 8 into TRs 15, 16 having the emitter area ratio of 1:n, the current amplification factor is increased to a multiple of (n).