Patent ID: 8571496

Claim:
A semiconductor device for signal amplification comprising: a ladder network including a plurality of cascade-coupled nodes to which an input signal supplied to an input node is transmitted, each node being weighted corresponding to the respective position in the ladder network and operable to generate a voltage of the correspondingly weighted input signal; a plurality of first transconductance amplifier stages arranged corresponding to each node of the ladder network, each of the first transconductance amplifier stages being operable to convert the voltage generated at the corresponding node to a current and to transmit the current to an output signal line arranged in common to the first transconductance amplifier stages; a logic control circuit operable to set the first transconductance amplifier stages to an enabled state selectively according to a control word; a current source circuit operable to generate a constant current unchangeable in temperature and to supply the constant current to the first transconductance amplifier stages so as to specify operating current of the first transconductance amplifier stages; a modulator circuit with a gain adjustable by a control signal, the modulator circuit operable to modulate a baseband signal to produce a modulated signal and to supply the modulated signal concerned to the ladder network as the input signal; a replica modulator circuit having the same structure as the modulator circuit, being coupled fixedly with a coupling path of a switching stage, having a gain adjustable by the control signal, and operable to modulate a first voltage with a fixed voltage level in simulation; at least one of replica amplifier having the same structure as the first transconductance amplifier stages and being operable to generate a signal corresponding to an output signal of the replica modulator circuit; and a differential amplifier circuit operable to generate the control signal by amplifying differentially the output signal of the replica amplifier and a second fixed voltage.