Variable capacitor circuit and integrated circuit containing the same
A technology of variable capacitors and integrated circuits, applied to single resonant circuits with only variable inductance/capacitance, electrical components, amplification control, etc.
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no. 1 example
[0073] FIG. 5 is a circuit diagram showing an integrated circuit 1a in which a variable gain amplifier 2 is integrated according to a first embodiment of the present invention.
[0074] The integrated circuit 1a of FIG. 5 is different from the integrated circuit 1 shown in FIG. 2A in that the circuit 40 is replaced by a voltage amplifier 40a having an input clamping function, and the variable capacitance circuit 60 is replaced by a variable capacitance circuit 60b. An inverter 321 is inserted in the switching signal line, and a buffer inverter 47 is added to provide a clamp pulse signal to the voltage amplifier 40a having an input clamp function. In this case, assuming that the variable gain amplifier 2 to be mounted is the first stage of an integrated circuit, the coupling capacitor 10 is not included in the variable gain amplifier 2 .
[0075] The voltage amplifier 40a has a clamp circuit 41a instead of the reference voltage source 41, and has an N-MOS transistor 42 with a g...
no. 2 example
[0088] FIG. 8 shows a circuit 60b in which a switch 62 (N-MOS transistor) is added to the variable capacitance circuit 60b. In the variable capacitance circuit 60c, a switch 62 is inserted between the input node 50 and the variable capacitance circuit 60b. The control signal Gmax / is supplied to the control terminal (gate) of the switch 62 . When the control signal Gmax / is low, the switch 62 is open and the amplification gain β is maximum. As mentioned above, when the control signal Gmax / is high, the switch 62 is closed, and the amplification gain β can be switched between two stages through the gain switching terminal Tg. Thus, in the second embodiment, with a single MOS capacitor, the amplification gain β can be switched between three stages.
no. 3 example
[0090] As above, an example in which the 2-stage variable voltage source 30 a is used to control the voltage Vc2 of the MOS capacitor 20 has been described in the above-described embodiment. In the third embodiment, the 2-stage variable voltage source 30a is replaced by a variable voltage source 30b shown in FIG. 10, which can set the voltage to selectable values within a predetermined range. Specifically, in the third embodiment, the variable voltage source 30b is connected to the one terminal 24 of the capacitor C2.
[0091] According to the third embodiment, the voltage applied from the variable voltage source 30b to one terminal 24 of the capacitor C2 is set at an optional value close to 0V (that is, the voltage is set at an optional value ranging from -Vca to Vcb) , and the capacitance value applied to the voltage amplifier 40a by the capacitor C2 can be finely adjusted to any value. That is, with a single capacitor C2, the gain of the voltage amplifier 40a can be fine...
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