Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-04-01
2001-02-27
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
C327S543000
Reexamination Certificate
active
06194955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a large scale integrated circuit (LSI), and more specifically to a CMOS LSI current source switch circuit for switching on and off an electric current to be provided from the current source of the LSI to a load.
2. Description of the Related Art
Various circuits such as a voltage control oscillator (VCO), a loop filter used for a phase locked loop (PLL), a timer using a time constant of an RC, etc. can control the current source of an LSI.
FIGS. 1 and 2
show the conventional technology of a current source switch circuit for switching on and off the electric current flowing from a current source to a load.
In the circuit shown in
FIG. 1
, a FET
11
functions as a switch for turning on and off the electric current provided from a MOS FET (current source)
10
which is connected to, for example, the ground side, and forms part of a current source; and a load
12
connected to, for example, an power supply are serially connected. When it becomes unnecessary to provide an electric current for the load
12
, the circuit shuts off the FET
11
according to a control signal input to the gate of the FET
11
, and the current source
10
is disconnected from the load
12
.
The circuit shown in
FIG. 2
is often used in a high-speed digital/analog converter, etc. In the circuit shown in
FIG. 2
, a FET
13
is connected between a power supply and a node N
1
, that is, between the current source
10
and the switch
11
. To the gate of the FET
13
, an inverter
14
provided by inverting the control signal provided for the gate of the switch
11
is connected. In this circuit, when it is not necessary that an electric current flows through the load
12
, the switch
11
is turned off according to the control signal, and the switch
13
is turned on. As a result, the electric current flowing through the current source
10
is returned to the power supply, that is, abandoned.
According to the first conventional technology shown in
FIG. 1
, the current source
10
is turned off by turning off the switch
11
. Therefore, it takes some time to reach a necessary value of the node N
1
to operate the current source
10
. Furthermore, the amount of the shift of an electric charge is large in switching on/off compared to the junction capacity of the FET. As a result, there has been the problem that a quick switch cannot be realized.
To solve the above described problem, according to the second conventional technology, the current source
10
is not turned off, and the shift of the electric charge to the junction capacity is minimized to a successful quick switch. However, this technology has the problem that it requires more electric power to operate the current source
10
even when it is not necessary to provide an electric current for the load
12
.
SUMMARY OF THE INVENTION
The present invention aims at providing a current source switch circuit for realizing a quick switch with smaller electric power.
The current source switch circuit according to the present invention requires at least a transistor forming part of a current source, and a switch for controlling the supply of an electric current from the transistor to a load. When an electric current is not provided by a switch for a load, the electric voltage having a value in an operating state as a current source is applied to the transistor (the supply of an electric current to the load is controlled by the switch).
By applying the voltage to the transistor, it becomes possible to keep the transistor operating in a saturation area. Thus, regardless of ON/OFF of the switch, the parasitic capacitance of the transistor is hardly charged or discharged. The rise time of the voltage when the switch is turned on can be very short. As a result, the electric current provided for the load becomes more stable, thereby realizing a quicker switch. Since a smaller amount of electric current flows through the entire circuit when no electric current flows through the load, less electric power is required.
REFERENCES:
patent: 4322636 (1982-03-01), Schroder
patent: 5825218 (1998-10-01), Colli et al.
patent: 5-48424 (1993-02-01), None
patent: 7-135452 (1995-05-01), None
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Zweizig Jeffrey
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