VARIABLE GAIN CIRCUIT AND TUNER SYSTEM PROVIDED WITH SAME

摘要

A variable gain transconductance amplifier includes an amplifier transistor connected to an input node, a cascode transistor having a source connected to a drain of the amplifier transistor and having a drain connected to an output node, and a switching circuit connecting or disconnecting a node to which the amplifier transistor and the cascode transistor are connected to or from a fixed potential in a switchable manner. A variable gain circuit may include the variable gain transconductance amplifier.

主权项

1. A variable gain circuit comprising:
a first path and a second path which are connected in parallel between an input terminal and an output terminal and which are capable of amplifying a signal, wherein, the first path has
a first variable attenuator connected to the input terminal, and attenuating an input signal by a variable amount of attenuation, anda first variable gain transconductance amplifier connected between the first variable attenuator and the output terminal, and amplifying an output from the first variable attenuator, the second path has
a second variable attenuator attenuating an input signal by a variable amount of attenuation, anda second variable gain transconductance amplifier connected between the second variable attenuator and the output terminal, and amplifying an output from the second variable attenuator, an input side of the second variable attenuator is connected to the input terminal or between the first variable attenuator and the first variable gain transconductance amplifier, and the first variable gain transconductance amplifier has a greater maximum gain than the second variable gain transconductance amplifier.