Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-12-05
2002-04-02
Mis, David (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S066000, C331S158000, C331S17700V
Reexamination Certificate
active
06366175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a temperature compensated oscillator, a control method for a temperature compensated oscillator, and a wireless communication device.
2. Description of Related Art
Conventionally, as oscillators used for electronic equipment, such as wireless communication devices, a temperature compensated oscillator (TCXO) is used because the output of frequency signals needs to be stable over a wide temperature range.
This temperature compensated oscillator utilizes the fact that oscillation frequency of a piezoelectric resonator changes according to the load capacity in order to maintain the oscillation frequency constant through a temperature compensation circuit in which the load capacity is varied according to temperature.
Also, among the temperature compensated oscillators, there are analog oscillators where the temperature compensation circuit is constructed by an analog circuit, and digital oscillators where the temperature compensation circuit is constructed by a digital circuit.
In an analog temperature compensated oscillator, because the temperature compensated circuit consists of many resistor elements and semiconductor elements, noise Vn is added to the temperature compensation voltage Vc
1
output by the temperature compensation circuit due to thermal noise, shot noise, and the like.
Therefore, in the analog temperature compensated oscillator shown in
FIG. 15
, by inserting a filter circuit
2
that removes the high-frequency component between a temperature compensation circuit
3
and a voltage controlled oscillation circuit
4
, noise Vn can be removed from the output voltage Vc
1
+Vn of the temperature compensation circuit
3
.
In this way, by installing the filter circuit
2
that removes noise contained in the temperature compensation voltage Vc
1
output from the temperature compensation circuit
3
, phase noise of the output signal is reduced.
FIG. 16
is a block diagram of a digital temperature compensated oscillator.
In a digital temperature compensated oscillator
10
, a temperature compensation circuit
11
consists, for example, of a temperature sensor
11
A, an analog/digital (AID) converter
11
B, a memory
11
C, and a digital/analog (D/A) converter
11
D.
In the temperature compensation circuit
11
, temperature information measured by the temperature sensor
11
A is converted from analog to digital by the A/D converter
11
B, converted to digital signal for compensating the temperature property of a piezoelectric resonator X memorized in advance in the memory
11
C, converted from digital to analog by the D/A converter
11
D, and output as temperature compensation voltage Vc
1
.
In this case, if any change occurs to the digital signal input to the D/A converter
11
D due to temperature change, step-shape noise Vn occurs to the temperature compensation voltage Vc
1
due to influence of resolution of the D/A converter
11
D.
Because of this, as shown in
FIG. 16
, by inserting the filter circuit
2
that removes the high-frequency component between the temperature compensation circuit
11
and the voltage controlled oscillation circuit (VCXO)
4
, noise Vn is removed from the temperature compensation voltage Vc
1
.
Therefore, by using a filter circuit such as an analog one in a digital temperature compensated oscillator, phase noise of the output signal can be reduced.
SUMMARY OF THE INVENTION
As in a property curve of a filter circuit (LPF), such as that shown in
FIG. 17
, the larger the time constant, namely the lower the cut-off frequency fc, the more decline high frequency shows in a filter circuit.
Because of this, for reducing phase noise of output signals of a temperature compensated oscillator using a filter circuit, it is better to set the cut-off frequency fc of the filter circuit low. Here, shown in
FIG. 18
is a property curve between the SSB phase noise at the detuning frequency and cut-off frequency fc of a filter circuit.
On the other hand, when power is supplied intermittently to a temperature compensated oscillator, from a power-saving point of view as in the standing-by time for a portable wireless communication device, reduction of time from the oscillation start until the output frequency becomes stable (called “Oscillation starting time” below) is desired.
However, as in a property curve of the oscillation starting time shown in
FIG. 19
, the lower the cut-off frequency of a filter circuit is set, the longer the oscillation starting time Tsta becomes.
Because of this, in a temperature compensated oscillator, there is a problem that realization of both reduction of phase noise of the output signal and reduction of the oscillation starting time is difficult.
Also, as shown in
FIG. 20
, common as an oscillator of modem portable wireless communication devices is a VC-TCXO that is equipped with a frequency control voltage input terminal VC for the frequency adjustment function that adjusts the frequency even more precisely based on the signal from the base station.
Namely, as shown in
FIG. 20
, VC-TCXO
12
inputs a frequency control signal &phgr;VC supplied to a signal processing circuit of a portable wireless communication device based on the signal received from the base station, and converts the voltage of this frequency control signal &phgr;VC to a frequency control voltage Vc
2
by a voltage conversion circuit
13
.
Then, in VC-TCXO
12
, the frequency control voltage Vc
2
and temperature compensation voltage Vc
1
are added by an adder
14
that is supplied to a voltage controlled oscillation circuit
4
via the filter circuit
2
. By this, frequency of the output signal is temperature compensated and changed to the frequency synchronous to the base frequency of the base station.
In the circuit described above, if phase noise of the output signal is reduced using a filter circuit
2
with a large time constant, a problem also occurs in that response of the oscillation frequency to the frequency control voltage Vc
2
is not good.
One objective of this invention is to at least provide a temperature compensated oscillator where phase noise of the output signal can be reduced, frequency of the output signal stabilizes in a short time, and response of the control is good. In accordance with various exemplary embodiments of this invention, a method of controlling and a wireless communication device equipped with this temperature compensated oscillator are provided.
In accordance with one exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, and a temperature compensation circuit that outputs temperature compensation voltage for keeping the oscillation frequency of the output signal constant based on temperature.
filter circuit that removes noise contained in the temperature compensation voltage;
switching circuit connected in parallel with the filter circuit; and
power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively,
wherein the power control circuit turns on the switching circuit for a specified period when power supply to the voltage controlled oscillation circuit is started.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, comprising;
filter circuit for removing noise contained in the temperature compensation circuit that is a low-pass filter where capacitance elements are connected in parallel to resistor elements via a switching circuit; and
power control circuit that controls power supply at least to the voltage controlled oscilla
Mis David
Oliff & Berridg,e PLC
Seiko Epson Corporation
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