| 摘要 |
PROBLEM TO BE SOLVED: To reduce variations in gain in a variable gain amplifier. SOLUTION: A temperature characteristic compensation circuit 12 generates a control current defined by K<SB>2</SB>.T-(K<SB>1</SB>.K<SB>2</SB>.T.V<SB>cont</SB>/K<SB>3</SB>) on the basis of a gain control current (K<SB>1</SB>.V<SB>count</SB>), a gain reference current (K<SB>3</SB>), and a bias current (K<SB>2</SB>.T). An exponential current generating circuit 21 is provided with a differential amplifier 13a having a pair of transistors, and the bases of each of the pair of transistors are connected to a base resistor 21, having a resistance value R. A control current is applied to the base of one of the transistors of the amplifier 13a, and the circuit 21 generates an exponential current, corresponding to the control current and controls a variable gain cell 14 according to the exponential current. In this case, the exponential current is defined as K<SB>2</SB>.T /[1+expäR.K<SB>2</SB>.T(1-K<SB>4</SB>.-V<SB>cont</SB>)/VT}] (VT=kT/q, where k is the Boltzmann constant, T is the absolute temperature and q is the electric charge). COPYRIGHT: (C)2003,JPO
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