Temperature compensated oscillator, its manufacturing method, and integrated circuit for temperature compensated oscillator

• US 20010048349A1
• Filed: 05/21/2001
• Published: 12/06/2001
• Est. Priority Date: 05/29/2000
• Status: Active Grant

• Current Assignee: Seiko NPC Corporation (Seiko Group)
• Original Assignee: Nippon Precision Circuits, Inc. (Seiko Group)
• Inventors: Matsumoto, Toru, Takahashi, Masayuki
• Granted Patent: US 6,515,548 B2
• Time in Patent Office: Days
• US Class Current: 331/25
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03L 1/025 and a memory for digitally storing correction values
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop

Abstract

An object of the invention is to provide a temperature compensated oscillator and reduce manufacture cost of this oscillator. Therefore, the temperature compensated oscillator has a frequency comparing circuit for comparing the frequency of an oscillating output signal of an oscillator circuit and the frequency of an external reference frequency signal externally inputted, and also has a sequential comparing register for determining each bit on the basis of results of this comparison. A digital signal from the sequential comparing register is set to an input of a D/A converter for generating a control voltage of a varicap diode. The temperature compensated oscillator performs a self compensating operation for sequentially determining each bit of the sequential comparing register every frequency comparison, and conforming the frequency of the oscillating output signal to that of the external reference frequency signal. The digital signal from the sequential comparing register is set to compensating data corresponding to a detecting temperature of a temperature detector at that time. The compensating data are determined by performing the self compensating operation every predetermined temperature change detected by the temperature detector.

Claims

1. A temperature compensated oscillator constructed by a temperature detector for outputting an analog signal according to temperature, an A/D converter for converting the analog signal from said temperature detector to a digital signal, a memory from which compensating data are read with the digital signal from said A/D converter as an address, a D/A converter for converting said compensating data from the digital signal to the analog signal, a variable capacity element being set the analog signal from said D/A converter as a control voltage of it, and an oscillator circuit for generating an oscillating output signal by oscillating a resonator such as a crystal resonator, and using said variable capacity element as a frequency adjusting element of said oscillating output signal;

said temperature compensated oscillator comprising a frequency comparing circuit for comparing frequencies of said oscillating output signal and an external reference frequency signal externally inputted, a register for sequentially determining a value of each bit of it on the basis of frequency comparing results of said frequency comparing circuit, and a switching circuit for selectively supplying the compensating data read from said memory and the digital signal outputted from said register to said D/A converter;

wherein said oscillator circuit performs an oscillating operation by supplying the digital signal outputted from said register to said D/A converter through said switching circuit;

the frequency of said oscillating output signal is changed by sequentially determining the value of each bit of said register on the basis of the comparing results of said frequency comparing circuit every comparing operation;

the frequency of the oscillating output signal of said oscillator circuit and the frequency of said external reference frequency signal are conformed to each other; and

the digital signal outputted from said register at a time when said frequency conforming occurs is written to said memory as said compensating data corresponding to a detecting temperature of said temperature detector every predetermined temperature step in a state in which the digital signal outputted from said A/D converter in accordance with said detecting temperature at that time is set to an address.

2. A temperature compensated oscillator according to

claim 1

, wherein said temperature step corresponds to a predetermined changing width of the detecting temperature of said temperature detector, and said temperature step is partitioned when the digital signal outputted from said A/D converter shows the predetermined changing width.

3. A temperature compensated oscillator according to

claim 1

or

2

, wherein said temperature step is narrowly set in a temperature range in which a temperature fluctuation of frequency accuracy of said oscillator becomes large.

4. A temperature compensated oscillator according to any one of

claims 1

to

3

, wherein said resonator is a crystal resonator, and said variable capacity element is a varicap diode.

6. A manufacturing method of a temperature compensated oscillator according to

claim 4

, wherein said temperature step corresponds to a predetermined changing width of the detecting temperature of said temperature detector, and said temperature step is partitioned when the digital signal outputted from said A/D converter shows the predetermined changing width.

5. A manufacturing method of a temperature compensated oscillator comprising:

a process for constructing a temperature compensated oscillator constructed by a temperature detector for outputting an analog signal according to temperature, an A/D converter for converting the analog signal from said temperature detector to a digital signal, a memory from which compensating data are read with the digital signal from said A/D converter as an address, a D/A converter for converting said compensating data from the digital signal to the analog signal, a variable capacity element being set the analog signal from said D/A converter as a control voltage of it, an oscillator circuit connected to a resonator such as a crystal resonator, and generating an oscillating output signal by performing an oscillating operation according to the resonator, and using said variable capacity element as a frequency adjusting element of said oscillating output signal, a frequency comparing circuit for comparing frequencies of said oscillating output signal and an external reference frequency signal externally inputted, a register for sequentially determining a value of each bit of it on the basis of frequency comparing results of said frequency comparing circuit, and a switching circuit for selectively supplying the compensating data read from said memory and the digital signal outputted from said register to said D/A converter;

a process for operating said temperature compensated oscillator at a predetermined specific temperature;

a process for inputting said external reference frequency signal to said frequency comparing circuit;

a process in which said oscillator circuit performs an oscillating operation by supplying the digital signal outputted from said register to said D/A converter through said switching circuit, and the frequency of said oscillating output signal is changed by sequentially determining the value of each bit of said register on the basis of the comparing results of said frequency comparing circuit every comparing operation, and the frequency of the oscillating output signal of said oscillator circuit and the frequency of said external reference frequency signal are conformed to each other;

a process for writing the digital signal outputted from said register at a time when said frequency conforming occurs to said memory as said compensating data corresponding to a detecting temperature of said temperature detector in a state in which the digital signal outputted from said A/D converter in accordance with said detecting temperature at that time is set to an address; and

a process for writing said compensating data required within a predetermined temperature compensating range to said memory by changing a circumferential temperature of said temperature compensated oscillator at a predetermined speed from said specific temperature so as to cross said predetermined temperature compensating range, and performing said writing operation of said compensating data every said predetermined temperature step.

7. A manufacturing method of a temperature compensated oscillator according to

claim 5

or

6

, wherein said temperature step is narrowly set in a temperature range in which a temperature fluctuation of frequency accuracy of said oscillator becomes large.

8. A manufacturing method of a temperature compensated oscillator according to any one of

claims 5

to

7

, wherein said resonator is a crystal resonator, and said variable capacity element is a varicap diode.

9. A manufacturing method of a temperature compensated oscillator according to any one of

claims 5

to

8

, wherein said specific temperature lies outside said predetermined temperature range.

10. An integrated circuit for temperature compensated oscillator comprising an A/D converter for converting an analog signal from a temperature detector for outputting the analog signal according to temperature to a digital signal, a memory from which compensating data are read with the digital signal from said A/D converter as an address, a D/A converter for converting said compensating data from the digital signal to the analog signal, a variable capacity element being set the analog signal from said D/A converter as a control voltage of it, an oscillator circuit externally attaching a resonator such as a crystal resonator thereto, and generating an oscillating output signal by oscillating the resonator, and using said variable capacity element as a frequency adjusting element of said oscillating output signal, a frequency comparing circuit for comparing frequencies of said oscillating output signal and an external reference frequency signal externally inputted, a register for sequentially determining a value of each bit of it on the basis of frequency comparing results of said frequency comparing circuit, and a switching circuit for selectively supplying the compensating data read from said memory and the digital signal outputted from said register to said D/A converter;

wherein said oscillator circuit performs an oscillating operation by supplying the digital signal outputted from said register to said D/A converter through said switching circuit;

the frequency of said oscillating output signal is changed by sequentially determining the value of each bit of said register on the basis of the comparing results of said frequency comparing circuit every comparing operation;

the frequency of the oscillating output signal of said oscillator circuit and the frequency of said external reference frequency signal are conformed to each other; and

the digital signal outputted from said register at a time when said frequency conforming occurs is written to said memory as said compensating data corresponding to a detecting temperature of said temperature detector every predetermined temperature step in a state in which the digital signal outputted from said A/D converter in accordance with said detecting temperature at that time is set to an address.

11. An integrated circuit for temperature compensated oscillation according to

claim 10

, wherein said temperature step corresponds to a predetermined changing width of the detecting temperature of said temperature detector, and said temperature step is partitioned when the digital signal outputted from said A/D converter shows the predetermined changing width.

12. An integrated circuit for temperature compensated oscillation according to

claim 10

or

11

, wherein said temperature step is narrowly set in a temperature range in which a temperature fluctuation of frequency accuracy of said oscillator becomes large.

13. An integrated circuit for temperature compensated oscillation according to any one of

claims 10

to

12

, wherein said resonator is a crystal resonator, and said variable capacity element is a varicap diode.