| 摘要 |
PURPOSE:To improve the SN ratio at the time of the weak input signal as well as the dynamic range by installing the control circuit which gives the control to the common emitter current of a pair of transistors Tr in the AGC circuit comprising the differential amplifier circuit. CONSTITUTION:Input Tr9 and constant current circuit 10 are connected to the common emitter of Tr7 and 8 forming the differential amplifier circuit. Furthermore, control circuit 11 is provided to control the emitter current of Tr7 and 8. When the input signal is small, emitter current I1 of Tr7 and 8 is fixed with no change to constant current I0 of circuit 10 via the control signal applied to terminal 19 of circuit 11. And collector current I2 of Tr7 decreases with increment of the input signal to prevent the lowering of the S/N ratio. When the input signal increases furthermore, current I1 becomes the sum of current I0 and current I3 of 2nd control current source 15 in accordance with the signal of terminal 19 in circuit 11, and current I1 increases. With increment of current I3, the input dynamic range of input Tr9 increases. |
