| 摘要 |
PROBLEM TO BE SOLVED: To minimize a gain drop and also to obtain a low noise characteristic by providing a detecting means detecting current and a 1st transistor which makes a control terminal a signal input and its 2nd terminal a signal output, etc., and realizing an accurate emitter degeneration resistance. SOLUTION: This circuit comprises a transistor 1, an FET 2 functioning as a variable resistance and a circuit 3 for compensation. Then, an external reference resistance 6 is connected to a transistor 4 between transistors 4 and 5 commonly connected to a base to which a bias is given by a bias generation circuit 11, resistances 8 and 9 are respectively connected between the collectors of the transistors 4 and 5 and a power source, the current difference between currents caused to flow to the both resistances is detected by potential difference, and an operational amplifier 10 applies feedback to the gate bias of a FET 7 and controls the gate voltage of the FET 2 for a variable resistance at the same time. Thus, an accurate emitter degeneration resistance is realized all the time even though there are fluctuations in a power supply voltage, temperature and an element value.
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