Semiconductor integrated circuit

Details Semiconductor integrated circuit Semiconductor integrated circuit

2000-12-19

2002-05-14

Shingleton, Michael B (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including differential amplifier

C330S257000, C330S261000, C330S311000

Reexamination Certificate

active

06388520

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-370603, filed Dec. 27, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor integrated circuit, and, more particularly, to a semiconductor integrated circuit with an amplifier circuit which has a wide dynamic range even for a low voltage source.
As the microminiaturization of the semiconductor process progresses, the state-of-the-art LSI circuit technology is demanded of a faster operational speed of integrated circuits, lower power consumption and lower supply voltages. While the improvement on the operational speed and the reduction in power consumption have been accomplished by the device technology, the circuit performance in lower supply voltages cannot be guaranteed by the device technology and should be achieved by the circuit technology.
In analog circuits, particularly, as the supply voltages become lower, it becomes difficult to improve the signal dynamic range and secure the good S/N (signal to noise) ratio. For example, a conventional amplifier circuit in a semiconductor integrated circuit shown in
FIG. 1A
comprises a basic OTA (Operational Transconductance Amplifier)
1
and a load resistor
2
as shown in FIG.
2
. Given that the mutual conductance of the OTA
1
is gm, the amplifier circuit outputs current i (=gm·Vin) proportional to an input voltage Vin. The current i is supplied to the load resistor
2
and Vin is amplified by gm·rL, yielding an amplified output voltage Vout.
The amplitude of the output voltage Vout that appears at an output terminal
101
is generally limited to (Vmax−Vmin) by voltage values Vmax and Vmin according to supply voltages (V
DD
, −V
SS
) as shown in FIG.
1
B. Therefore, the reduction in supply voltages reduces the dynamic range of an analog signal Vout, thus making it difficult to secure the performance of the amplifier circuit.
Conventionally, various attempts have been made to reduce the supply voltages. The attempts include the generation of a high voltage by a booster circuit (DC-DC converter, boost trap circuit or the like), and designing a folded type circuit or a low-voltage circuit which uses MOS transistors having a low threshold value. The booster circuit raises a problem of a breakdown voltage in the microminiaturization or sub-micron process. The folded type circuit generally suffers a complicated circuit design. MOS transistors with a low threshold value often produce a leak current which should be coped with. Those techniques often stand in the way of designing an analog circuit into an integrated circuit in the microminiaturization process, and do not always provide a solution to securing the dynamic range in analog signal processing.
Apparently, as the supply voltages become lower, it becomes difficult to improve the signal dynamic range and secure the good S/N ratio in accordance with the reduction in supply voltages. In an amplifier circuit, particularly, the reduction in supply voltages reduces the dynamic range of an analog signal. This makes it difficult to secure the performance of the amplifier circuit.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor integrated circuit that can realize an amplifier circuit having a wide effective dynamic range even for low supply voltages and that can realize an amplifier circuit having a wide dynamic range using the ordinary CMOS semiconductor circuit technology.
According to a first aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a load resistor having one end connected to an output terminal of the current output type amplifier and a voltage control circuit having an input terminal connected to the one end of the load resistor and an output terminal connected to the other end of the load resistor, an input terminal of the amplifier circuit serving as an input terminal of the current output type amplifier, output terminals of the amplifier circuit serving as the individual ends of the load resistor.
The following are preferable embodiments of the first aspect of the invention.
(1) The voltage control circuit comprises a first functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is higher than the first constant voltage and operates as an inverting operational amplifier when the input voltage is lower than the first constant voltage.
(2) The voltage control circuit comprises a second functional circuit which fixes an output voltage to a preset second constant voltage when an input voltage is lower than the second constant voltage and operates as an inverting operational amplifier when the input voltage is higher than the second constant voltage.
(3) The voltage control circuit comprises a third functional circuit which operates as an inverting operational amplifier.
According to a second aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a first resistor having one end connected to an output terminal of the current output type amplifier, a first voltage control circuit having an input terminal connected to the one end of the first resistor, a second resistor having one end connected to the output terminal of the current output type amplifier, and a second voltage control circuit having an input terminal connected to the one end of the second resistor and an output terminal connected to the other end of the second resistor. The amplifier circuit has an input terminal serving as an input terminal of the current output type amplifier and output terminals serving as the output terminal of the current output type amplifier and the other ends of the first and second resistors.
The second aspect of the present invention may take the form of the following preferable embodiment.
The second voltage control circuit comprises a first functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is higher than the first constant voltage and operates as an inverting operational amplifier when the input voltage is lower than the first constant voltage, and the first voltage control circuit is constituted by a second functional circuit which fixes the output voltage to a preset second constant voltage higher than the first constant voltage when the input voltage is lower than the second constant voltage and operates as an inverting operational amplifier when the input voltage is higher than the second constant voltage.
According to a third aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a first resistor having one end connected to an output terminal of the current output type amplifier, a first voltage control circuit having an input terminal connected to the one end of the first resistor, a second resistor having one end connected to the output terminal of the current output type amplifier, and a third voltage control circuit having an input terminal connected to the other end of the first resistor and an output terminal connected to the other end of the second resistor. The amplifier circuit has an input terminal serving as an input terminal of the current output type amplifier and output terminals serving as the output terminal of the current output type amplifier and the other ends of the first and second resistors.
The following are preferable embodiments of the third aspect of the invention.
(1) The first voltage control circuit c

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