Semiconductor device for signal amplification

1. 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; and

a logic control circuit operable to set the first transconductance amplifier stages to an enabled state selectively according to a control word.

2. The semiconductor device for signal amplification according to claim 1 further comprising:

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.

3. The semiconductor device for signal amplification according to claim 2 ,

wherein the modulator circuit includes:

a baseband signal input stage operable to receive the baseband signal;

a switching stage coupled to the baseband signal input stage and operable to switch over a transmission path of an output signal of the baseband signal input stage;

a gain control stage coupled to the switching stage and operable to adjust a gain of a signal transmitted from the switching stage and operable to transmit the signal to an output node, and

wherein the gain control stage, the switching stage, and the baseband signal input stage are coupled between the output node and the current source in a manner mutually stacked in vertical structure.

4. The semiconductor device for signal amplification according to claim 3 ,

wherein the replica amplifier includes a plurality of replica amplifiers arranged corresponding to each of the first transconductance amplifier stages, and

wherein the logic control circuit enables a replica amplifier arranged corresponding to the first transconductance amplifier stage which is in an enabled state and generates a current signal with the maximum amplitude among the first transconductance amplifier stages.

5. The semiconductor device for signal amplification according to claim 1 ,

wherein the ladder network includes:

a plurality of first impedance components coupled in series to the input node receiving the input signal; and

a plurality of second impedance components arranged corresponding to the first impedance components and coupled to the corresponding first impedance component in parallel,

wherein each of the second impedance components has a first sub impedance component and a second sub impedance component coupled in series, and

wherein each transconductance amplifier stage receives a signal at a connection node between the corresponding first sub impedance component and the corresponding second sub impedance component.

6. The semiconductor device for signal amplification according to claim 1 further comprising:

at least one of second transconductance amplifier stage coupled to the input node and enabled selectively according to the control word, and in an enabled state, operable to transmit a current corresponding to an input signal at the input node to the output signal line,

wherein the second transconductance amplifier stage has different transconductance from the first transconductance amplifier stage.