Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-05-12
2001-09-18
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S054000, C327S065000
Reexamination Certificate
active
06292032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high impedance circuit used as, for example, a signal input circuit, and particularly relates to a high impedance circuit and a high gain amplifier which are suitably used as a signal input circuit for a high frequency signal, such as a radio receiver, a television receiving set, a satellite broadcasting receiver, a video recorder and a mobile communication device.
2. Description of the Related Art
It is necessary that a signal input circuit has a high impedance. In addition, since a high speed operation is required to a signal input circuit used for a high frequency signal such as a signal for a radio receiver, a video signal for a television receiving set, a high frequency signal for a satellite broadcasting receiver, a video signal for a video recorder and an RF signal for a mobile communication device, normally such circuit is formed as a high impedance circuit having a differential-pair type circuit.
As a background art of the high impedance circuit of-the present invention, an example of a differential-pair type high impedance circuit having a differential-pair circuit which is suitable to a signal input circuit for a high frequency signal will be explained below with reference to FIG.
1
.
FIG. 1
is a circuit diagram of a differential-pair type high impedance circuit as a background art of the high impedance circuit of the present invention.
This differential-pair type high impedance circuit comprises npn-type transistors Q
11
and Q
12
composing a differential-pair type circuit, both of the emitters are commonly connected and grounded to the ground potential GND via a resistance element R
10
. Bases of the npn-type transistors Q
11
and Q
12
are commonly connected and further connected to resistance elements R
11
and R
12
. The high impedance circuit further comprises an npn-type transistor Q
13
whose base is connected to the collector of the npn-type transistor Q
11
and the emitter is connected to the base of the npn-type transistor Q
11
via a current source circuit I
11
and the resistance element R
11
, and an npn-type transist or Q
14
whose base is connected to the collector of the npn-type transistor Q
12
and the emitter is connected to the base of the npn-type transistor Q
12
via the current source circuit I
11
and the resistance element R
12
.
The high impedance circuit further comprises pnp-type transistors Q
21
and Q
22
connected to the collectors of the npn-type transistors Q
11
and Q
12
, and resistance elements R
21
and R
22
connected between the transistors Q
21
and Q
22
and a first potential power source line Vcc in order that the differential-pair type circuit becomes high impedance. The base of the transistor Q
21
and the base of the transistor Q
22
are commonly connected. These pnp-type transistors Q
21
and Q
22
and the resistance elements R
21
and R
22
function as a direct current (DC) power source for the differential-pair type circuit.
The high impedance circuit is further provided with pnp-type transistors Q
23
and Q
24
, resistance elements R
23
and R
24
connected to the emitters of these pnp-type transistors Q
23
and Q
24
, and a current source circuit I
12
for these circuits.
In this high impedance circuit, an input impedance Zin looked from the npn-type transistor Q
13
is very high.
In the high impedance circuit shown in
FIG. 1
, the high impedance components depend on collector impedance of the transistors Q
11
and Q
12
, that is, the impedance by circuits such as the pnp-type transistors Q
21
and Q
22
. Accordingly, a bias is needed for providing direct current (DC) power sources at upper and under portions of the differential-pair type circuit in the high impedance circuit. Due to the bias, there arises a scale reduction of a dynamic range of more than about 1V, on the voltage of the first potential power source Vcc and the second potential power source GND. As a result, this high impedance circuit is not suitable for a low voltage operation.
Particularly, in a recent high impedance circuit for a high frequency signal, a wide dynamic range and operation at further lower voltage are required, therefore, the above disadvantage may be become large on a high impedance circuit for a high frequency operation.
Also, since the npn-type transistors Q
11
to Q
14
are used together with the pnp-type transistors Q
21
to Q
24
having an opposite polarity in the high impedance circuit in
FIG. 1
, it becomes complicated when manufacturing one integrated circuit (IC) accommodating these circuits.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high impedance circuit operatable at a low voltage and whose dynamic range is not reduced.
Another object of the present invention is to provide a high impedance circuit easy to be manufactured and suitable for forming an IC.
According to the present invention, there is provided a high impedance circuit, comprising; a first transistor, a first resistance element connected between one terminal of the first transistor and a first voltage power supply line, a first current source connected between another terminal of the first transistor and a second voltage power supply line, a second transistor having a characteristic same as that of the first transistor, a second resistance element connected between one terminal of the second transistor and the first voltage power supply line and having a resistance value same as that of the first resistance element, a second current source connected between another terminal of the second transistor and the second voltage power supply line and having a characteristic same as that of the first current source, a third resistance element connected between another terminal of the first transistor and another terminal of the second transistor, a first buffer circuit element connected between the one terminal of the second transistor and a control terminal of the first transistor, and a second buffer circuit element connected between the one terminal of the first transistor and a control terminal of the second transistor, and a half of a resistance value of the third resistance element being larger than and close to a resistance value of the respective first resistance element and second resistance element.
Working of a Basic High Impedance Circuit
The above first and second transistors compose a differential-pair type circuit. In this differential-pair type circuit, the first and the second buffer circuits serve as a direct current (DC) bias circuit. Furthermore, in order that the third resistance element connected between the other ends of the first and the second transistors feedbacks as a negative resistance, a control terminal of transistors in the differential-pair type circuit, for example, a base voltage is bias-shifted to one terminal of transistors in differential-pair type circuit, for example, to a collector. Namely, the high impedance circuit of the present invention operates as a current feedback circuit.
In order that the high impedance circuit of the present invention has as large impedance as possible, it is preferable to set the resistance value (R
2
) of the first resistance element (R
2
) and the second resistance element (R
2
) larger than half the resistance value of the third resistance element (
2
R
1
) and, at a time, close to the value of the first resistance element (R
2
) and the second resistance element (R
2
).
Preferably, the first transistor is an npn-type bipolar transistor, and the second transistor is an npn-type bipolar transistor.
Preferably, the first buffer circuit element includes a third transistor, whose one base is connected to a collector of the second transistor and an emitter is connected to a base of the first transistor, and having a same conductivity of the first transistor, and a third current source circuit connected between an emitter of the third transistor and the second voltage source, and wherein the second buffer circuit element includes a fourth transistor, whose one base is connect
Fujita Kosuke
Hirabayashi Atsushi
Komori Kenji
Murayama Norihiro
Cunningham Terry D.
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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