| 摘要 |
PURPOSE:To improve the dynamic offset by using a current control circuit which drives a current mirror circuit that working as an active load to a variable gain amplifier with a control signal and a current adversely proportional to a drive current. CONSTITUTION:For a variable gain amplifier 2, the transistors TR Q3 and Q4 perform the amplifying operations and a TR Q5 controls a current Io corresponding to a control current ICONT. An output current Iout corresponding to Io/2-i is obtained from a current mirror circuit 3. At the same time, an output current Iout' corresponding to Io/2+i is obtained from a current mirror circuit 4. The TR Q12, Q13 and Q14 form a current mirror circuit 6 and suck a current of (Iout'-Iout). As a result, the DC components of reference currents IX and IY of both circuits 3 and 4 are set at an approximately fixed current value regardless of the level of the current ICONT. Then, the dynamic offset of an output signal Vout is improved. |
