Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-03-30
2001-09-18
Mis, David (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S03600C, C331S17700V, C333S214000
Reexamination Certificate
active
06292064
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a voltage controlled oscillator (VCO) and semiconductor integrated circuit (IC) device, and more particularly, to a compact voltage controlled oscillator comprising a field-effect transistor (FET) IC.
2. Description of the Related Art
Recent developments in the field of mobile communications devices, in particular cellular telephones, mobile communications equipment and cordless telephones, have resulted in rapid reductions in both the size and price of such equipment. As a result, there is an ever-increasing need to reduce the number of component parts of such devices as well as to reduce the unit costs of such parts. It is for these reasons that the need has arisen to include the voltage controlled oscillator (hereinafter referred to as a VCO) used as a modulation/demodulation circuit in such devices within a complementary metal-oxide semiconductor (CMOS) integrated circuit (IC).
The following can be given as an example of a conventional VCO.
FIG. 1
is a circuit diagram of a conventional VCO
100
, in this case a Colpitts type VCO
100
using a bipolar transistor
101
. The VCO
100
comprises the bipolar transistor
101
as well as condensers
102
,
103
,
104
,
105
, a resistor
108
, an inductor
106
and a varicap
107
. A collector of the transistor
101
is connected to one terminal of the resistor
108
, the other terminal of the resistor
108
being connected to a power source
109
.
An emitter of the transistor
101
is connected to one terminal of condenser
102
. The other terminal of the condenser
102
is connected to one terminal of condenser
103
and a base of transistor
101
. One terminal of condenser
104
is connected to the base of transistor
101
, the other terminal of condenser
104
being connected to one terminal of condenser
105
and one terminal of inductor
106
. The other terminal of inductor
106
is connected to a ground
110
. The other terminal of condenser
105
is connected to a cathode of varicap
107
, an anode of varicap
107
being connected to the ground
110
. A control voltage
111
is applied at the point of connection between the condenser
105
and the cathode of the varicap
107
. By inputting a control voltage
111
at the junction between the condenser
105
and the varicap
107
a voltage applied to the varicap
107
is controlled, the capacitance of the varicap
107
is changed and the oscillation frequency is changed.
FIG. 2
is a diagram for the purpose of describing a conventional CMOS ring-type VCO
200
, in which the CMOS inverters are connected in a ring. An NMOS transistor
201
and a PMOS transistor
204
form the first inverter, an NMOS transistor
202
and a PMOS transistor
205
form the second inverter, and an NMOS transistor
203
and a PMOS transistor
206
form the third inverter. An output
211
of the first inverter formed by the NMOS transistor
201
and the PMOS transistor
204
is connected to a gate of NMOS transistor
202
, an output
212
of the second inverter formed by the NMOS transistor
202
and the PMOS transistor
205
is connected to a gate of NMOS transistor
202
, and an output
210
of the third inverter formed by the NMOS transistor
203
and the PMOS transistor
206
is connected to a gate of NMOS transistor
201
, thus connecting in a shape of a ring.
The gates of PMOS transistors
204
,
205
,
206
are jointly connected and are controlled by a control voltage
209
. The current flowing through PMOS transistors
204
,
205
,
206
is controlled according to the value of the control voltage
209
, thus controlling the extent of the delay of each of the inverters connected in the ring and controlling the oscillation frequency.
FIG. 3
is a diagram for the purpose of describing a conventional CMOS inverter VCO, in which the VCO
300
uses CMOS inverters. The VCO
300
comprises an inverter
301
, resistor
302
, condenser
303
, crystal resonator
304
, condenser
305
, varicap
306
and resistor
307
. The resistor
302
and crystal resonator
304
are connected to an input terminal and an output terminal of the inverter
301
. The condenser
303
is connected between the output terminal of the inverter
301
and the ground. One terminal of the condenser
305
is connected to the input terminal of the inverter
301
and the other terminal of the condenser
305
is connected to a cathode of the varicap
306
. An anode of the varicap
306
is connected to the ground.
One terminal of the resistor
307
is connected to the point of connection between the condenser
305
and the varicap
306
, a control voltage
308
being applied to the other terminal of the resistor
307
. By controlling the voltage applied to the varicap
306
from the control voltage
308
, the capacitance of the varicap
306
is changed and the oscillation frequency of the output signal of the inverter
309
is changed as well.
However, the conventional voltage controlled oscillators described above have the following problem.
The Colpitts type VCO
100
using the bipolar transistor
101
shown in
FIG. 1
uses the varicap diode
107
. Forming this varicap diode
107
on a semiconductor chip would require a large surface area and would make large-scale integration impractical. Additionally, the varicap diode
107
is difficult to form using the CMOS process widely used for current logic circuits. That is, without using a mixed bipolar/CMOS process the VCO
100
cannot be formed on the same chip as the logic circuit. As a result, in order to form the VCO
100
on the same semiconductor chip as the logic circuit, a mixed bipolar/CMOS process is used. However, such a mixed bipolar/CMOS process complicates the production process and increases the cost of the IC so produced.
Additionally, the CMOS ring-type VCO
200
shown in
FIG. 2
, in which an odd number of individual CMOS inverters are connected in rings, has the following problem.
The individual NMOS transistors
201
,
202
,
203
basically operate at saturation, so a rectangular oscillating wave is the form of the oscillator output
210
. Since the wave form is a rectangular wave, distortion is high and the carrier-to-noise ratio (C/N) is low.
Moreover, the VCO
300
using the CMOS inverter
301
shown in
FIG. 3
has the following problem.
The VCO
300
shown in
FIG. 3
uses the crystal resonator
304
. As a result, changing the control voltage
308
from a minimum value near ground level to a maximum value near the supply voltage only changes the frequency by about 10 kHz, so the operating range is narrow.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide an improved and useful a voltage controlled oscillator (VCO) and semiconductor integrated circuit (IC) device, wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a VCO capable of being formed by a CMOS process, having a small surface area, a high oscillation signal C/N ratio, low distortion and broad operating frequency range.
The above-described objects of the present invention are achieved by a voltage controlled oscillator (VCO) having an amplifier including a field-effect transistor (FET), the VCO comprising a voltage controlled capacitor, the voltage controlled capacitor comprising an inversion amplifier comprising an FET, an amp gain of the inversion amplifier being controlled by a voltage; and a capacitor connected between an input and an output of the inversion amplifier.
According to the invention described above, the oscillation frequency can be can be controlled, thus making it possible to provide a VCO formed from FETs from which an oscillating sine wave form can be obtained.
Additionally, the above-described objects of the present invention are also achieved by a semiconductor semiconductor integrated circuit (IC) device including a voltage controlled oscillator (VCO) having an amplifier including a field-effect transistor (FET), the VCO comprising a voltage controlled capacitor, the voltag
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Mis David
LandOfFree
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