Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-12-15
2001-07-24
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S081000
Reexamination Certificate
active
06265909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-valued switching circuit having one input terminal and one output terminal to obtain output with three kinds of current values from one output terminal.
2. Description of the Related Art
With reference to
FIG. 17
, a conventional current switching circuit will be described. In
FIG. 17
, the current switching circuit includes two current sources
92
and
93
connected to a current mode circuit
91
, and switches SW
1
and SW
2
for switching these current sources
92
and
93
. The current sources
92
and
93
have current values of IO and IO/2, respectively. To a control input terminal
94
, a low level or high level control input signal is applied. This control input signal is supplied, as a switching signal of the switches SW
1
and SW
2
, through an inverter
95
to the switch SW
2
and further through an inverter
96
to the switch SW
1
.
The current switching circuit is structured to have two current sources to be switched by the switches SW
1
and SW
2
for attaining different electrical characteristics by changing a current value of the current mode circuit
91
. More specifically, one of the two current sources
92
and
93
can be selected by selecting the switch SW
1
or the switch SW
2
in response to one control input signal at a logical high or low level.
The above-described current switching circuit, however, requires current sources and switches to be prepared as many as the number of current values to be varied.
On the other hand, a three-valued logic circuit enabling one current source to have three kinds of output is known (e.g. Utility Model Laying-Open No. 2-6684). In the three-valued logic circuit, output is allotted to one of three output terminals according to three kinds of potentials applied to an input terminal and three output terminals are accordingly needed. Output currents of the three output terminals are the same.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a three-valued switching circuit enabling output with three kinds of current values to be taken out by a logical value signal applied to one control input terminal.
Other object of the present invention is to realize simplification of bias setting of a switching circuit.
According to one aspect of the invention, a three-valued switching circuit, comprises
one control input terminal and one output terminal,
at least two transistors constituting a differential pair, and
one constant current source connected to a common emitter terminal of the at least two transistors, wherein
a collector of one of the at least two transistors is connected to the output terminal to output three kinds of current values from the output terminal in response to a three-valued logic control signal applied to the control input terminal.
In the preferred construction, when a current value of the constant current source is IO, the three kinds of current values take one of IO, (1/2)·IO and 0.
In another preferred construction, a current mirror circuit is connected at the output side to reflect an output current and supply the current to a current mode circuit connected to a terminal of a power source.
In another preferred construction, when a current value of the constant current source is IO, the three kinds of current values take one of IO, (1/2)·IO and 0, and a current mirror circuit is connected at the output side to reflect an output current and supply the current to a current mode circuit connected to a terminal of a power source.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, and a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal, and a current mirror circuit is connected at the output side to reflect an output current and supply the current to a current mode circuit connected to a terminal of a power source.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal, and when a current value of the constant current source is IO, the three kinds of current values take one of IO, (3/4)·IO and (1/2)·IO.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal, a current mirror circuit is connected at the output side to reflect an output current and supply the current to a current mode circuit connected to a terminal of a power source, and when a current value of the constant current source is IO, the three kinds of current values take one of IO, (3/4)·IO and (1/2)·IO.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal, and a transistor ratio of the three transistors is arbitrarily changed like A: B: C: (A, B and C are integers) to take out an output current value.
In another preferred construction, one transistor is added to the two transistors constituting a differential pair to make three-transistor structure, all emitters of the three transistors are connected to the constant current source, the other of the two transistors and the additional transistor have bases commonly connected to the control input terminal, a base of one of the two transistors is connected to a reference voltage source, a collector of the one transistor and a collector of the additional transistor are commonly connected to the output terminal, a current mirror circuit is connected at the output side to reflect an output current and supply the current to a current mode circuit connected to a terminal of a power source, and a transistor ratio of the three transistors is arbitrarily changed like A: B: C: (A, B and C are integers) to take out an output current value.
In another preferred construction, a th
NEC Corporation
Nu Ton My-Trang
Scully Scott Murphy & Presser
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