Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2001-08-06
2002-12-17
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06496057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant current generation circuit for generating a constant current, a constant voltage generation circuit for generating a constant voltage, a constant voltage/constant current generation circuit for generating a constant voltage and a constant current, and an amplification circuit using the same.
2. Description of the Background Art
Reference current generation circuits for generating constant reference currents and reference voltage generation circuits for generating constant reference voltages are used for various analog circuits. In ALPC (Auto Laser Power Control) circuits and A/D (Analog-to-Digital) converters for CD (Compact Disk) drives, for example, constant voltage generation circuits for generating constant reference voltages which do not depend on the variation in power supply voltage, the temperature change, and the variation in processes are required.
On the other hand, frequency characteristics of operational amplifiers greatly depend on bias currents. If the bias currents are constant, the dependency on the variation in power supply voltage, the temperature change, and the variation in processes can be reduced, thereby making it possible to realize high-performance analog circuits. From such a point of view, constant current generation circuits are important in order to supply constant bias currents.
In recent years, the above-mentioned analog circuits such as the ALPC circuits, the A/D converters, and the operational amplifiers have been made one chip using the CMOS (Complementary Metal-Oxide Semiconductor) process. In this case, the constant voltage generation circuits and the constant current generation circuits must be designed by CMOS circuits.
Currents generated by the constant current generation circuits using the CMOS circuits vary by the variation in power supply voltage, the temperature change, and the variation in processes. The amount of the variation in this case is significantly large.
FIG. 8
is a circuit diagram showing an example of a conventional constant current generation circuit.
The constant current generation circuit shown in
FIG. 8
is constituted by p-channel MOS field effect transistors
81
,
82
, and
87
, n-channel MOS field effect transistors
83
,
84
,
85
, and
86
, and a resistor
88
.
The transistor
81
has its source connected to a power supply terminal receiving a power supply voltage, has its drain connected to a node N
81
, and has its gate connected to a node N
82
. The transistor
82
has its source connected to the power supply terminal, and has its drain and its gate connected to the node N
82
. The transistor
83
has its drain connected to the node N
81
, has its source connected to a node N
83
, and has its gate connected to a node N
84
. The transistor
84
has its drain connected to the node N
82
, has its source connected to the node N
84
, and has its gate connected to the node N
81
.
The transistor
85
has its drain connected to the node N
83
, has its source connected to a ground terminal, and has its gate fed with an inverted stand-by signal STB. The transistor
86
has its drain connected to the node N
84
through the resistor
88
, has its source connected to the ground terminal, and has its gate fed with the inverted stand-by signal STB. The transistor
87
has its source connected to the power supply terminal, has its gate connected to the node N
82
, and has its drain supplied with a current IC.
The transistors
81
and
82
constitute a current mirror circuit, and a current which is equal or proportional to a current flowing through the transistor
81
flows through the transistor
82
.
In the constant current generation circuit shown in
FIG. 8
, when the inverted stand-by signal STB enters a high level, the transistors
85
and
86
are turned on. Consequently, a current Ir flows from the power supply terminal to the ground terminal through the transistors
82
and
84
, the resistor
88
, and the transistor
86
.
A current It which is equal or proportional to the current Ir flows from the power supply terminal to the ground terminal through the transistors
81
,
83
, and
85
. In this case, a voltage applied across both ends of the resistor
88
is uniquely determined by a gate-source voltage of the transistor
83
. Consequently, a constant voltage is applied across both ends of the resistor
88
irrespective of the power supply voltage. Therefore, the current Ir flowing through the resistor
88
does not depend on the variation in the power supply voltage.
In this case, the current Ir flowing through the resistor
88
is determined by the following equation:
Ir=Va/R
=&bgr;·(
Va−Vt
)
2
(A1)
Here, Va denotes a voltage applied across both ends of the resistor
88
, that is, the gate-source voltage of the transistor
83
, Vt denotes a threshold voltage of the transistor
83
, and R denotes the resistance value of the resistor
88
. Further, &bgr; is expressed by the following equation:
&bgr;=(½)·(
W/L
)·Cox·&mgr; (A2)
In the foregoing equation (A2), W denotes the gate width of the transistor
83
, L denotes the gate length of the transistor
83
, Cox denotes the capacitance of a unit oxide film of the transistor
83
, and &mgr; denotes the mobility of electrons or holes.
Conventionally, a bias voltage has been set such that the gate-source voltage of the transistor
83
is approximately equal to the threshold voltage Vt.
As described in the foregoing, in the constant current generation circuit shown in
FIG. 8
, the current IC is constant without depending on the variation in the power supply voltage. However, &bgr;, Vt, and R in the foregoing equation (A2) vary depending on the variation in processes, and the current Ir and the voltage Va also vary depending on the temperature change. Consequently, it is impossible to obtain a constant current which does not depend on the temperature change and the variation in processes.
When a constant voltage generation circuit for generating a constant voltage is constructed using a CMOS circuit, a constant current generated by the constant current generation circuit is generally converted into a constant voltage using a resistance load. When the constant voltage generation circuit is constructed using the constant current generation circuit shown in
FIG. 8
, the current IC is converted into a voltage using the resistor. Also in this case, the current IC varies by the temperature change and the variation in processes. Accordingly, it is impossible to obtain a constant voltage which does not depend on the temperature change and the variation in processes.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a constant current generation circuit composed of a field effect transistor and capable of generating a constant current without depending on the variation in power supply voltage and the temperature change.
Another object of the present invention is to provide a constant current generation circuit composed of a field effect transistor and capable of generating a constant current without depending on the variation in power supply voltage, the temperature change, and the variation in processes.
Still another object of the present invention is to provide a constant voltage generation circuit composed of a field effect transistor and capable of generating a constant voltage without depending on the variation in power supply voltage, the temperature change, and the variation in processes.
A further object of the present invention is to provide a constant voltage/constant current generation circuit composed of a field effect transistor and capable of generating a constant current and a constant voltage without depending on the variation in power supply voltage, the temperature change, and the variation in processes and an amplification circuit using the same.
A constant current generation circuit according to an aspect of the present invention comprises a first field effect transistor having a
Tani Kuniyuki
Wada Atsushi
Armstrong Westerman & Hattori, LLP
Sanyo Electric Co,. Ltd.
Zweizig Jeffrey
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