TEMPERATURE-COMPENSATED CRYSTAL OSCILLATOR BASED ON DIGITAL CIRCUIT

Abstract

The present invention provides a temperature-compensated crystal oscillator based on digital circuit, a closed-loop compensation architecture is employed to realize the high precision compensation of the crystal oscillator. The output frequency f(T) of the TCXO to be compensated is directly connected with the compensation voltage V.sub.c(T) in real time, and the compensation voltage is fed back to the voltage control terminal of the VCXO to be compensated to compensate, so that the output frequency after compensation is equal to the target frequency signal, thus avoiding the frequency shift of output signal caused by temperature hysteresis, i.e. the discrepancy between the temperature acquired by a temperature senor and the real temperature of the resonant wafer in the prior art.

Claims

1. a temperature-compensated crystal oscillator based on digital circuit, comprising: a VCXO for generating a signal with desired frequency; a compensation network for generating a desired compensation voltage based on a compensation voltage value and sending the desired compensation voltage to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency; wherein further comprising a power divider, an analog-to-digital converter and a microprocessor; where the power divider divides the signal with desired frequency signal into two signals: one is used as the output of the TCXO and the other is sent to the analog-to-digital converter; the analog-to-digital converter converts the signal with desired frequency into a corresponding frequency value with binary form, and sends the corresponding frequency value to the microprocessor; a binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled is stored in the microprocessor, the microprocessor finds a compensation voltage value in the binary coding table according to the frequency value sent by the analog-to-digital converter, and sends it to the compensation network.

2. A TCXO based on digital circuit of claim 1, wherein the compensation network comprises a digital-to-analog converter, a signal conditioning circuit and a filter, the digital-to-analog converter converts the compensation voltage value into a corresponding analog voltage signal, and the signal conditioning circuit modulates the analog voltage signal to generate a compensation voltage V.sub.c(T), the filter filters the compensation voltage V.sub.c(T), and sends the compensation voltage V.sub.c(T) to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0032] The above and other objectives, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0033] FIG. 1 is a diagram of a TCXO based on digital circuit in prior art;

[0034] FIG. 2 is a diagram of a TCXO based on digital circuit according to one embodiment of the present invention;

[0035] FIG. 3 is a diagram of an acquisition system for obtaining a binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the similar modules are designated by similar reference numerals although they are illustrated in different drawings. Also, in the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.

[0037] FIG. 2 is a diagram of a TCXO based on digital circuit according to one embodiment of the present invention.

[0038] in one embodiment, as shown in FIG. 2, the TCXO based on digital circuit comprises a voltage controlled crystal oscillator, i.e. VCXO 1, a compensation network 2, a power divider 3, an analog-to-digital converter 4 and a microprocessor 5;

[0039] The VCXO 1 generates a signal with desired frequency, and the power divider 3 divides the signal with desired frequency into two signals, one is used as the output of the TCXO and the other as input is sent to the analog-to-digital converter 4. the analog-to-digital converter 4 converts the signal with desired frequency into a corresponding frequency value with binary form, and sends the frequency value to the microprocessor 5, the microprocessor 5 has a pre-stored binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled, the microprocessor 5 finds a compensation voltage value in the binary coding table according to the frequency value sent by the analog-to-digital converter and sends it to the compensation network 2. The compensation network 2 generates a desired compensation voltage based on a compensation voltage value and sends the desired compensation voltage to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency;

[0040] In one embodiment, as shown in FIG. 2, the compensation network 2 comprises a digital-to-analog converter 201, a signal conditioning circuit 202 and a filter 203. The digital-to-analog converter 201 converts the compensation voltage value into a corresponding analog voltage signal, and the signal conditioning circuit 202 modulates the analog voltage signal to generate a compensation voltage V.sub.c(T). The filter 203 filters the compensation voltage V.sub.c(T), and sends the compensation voltage V.sub.c(T) to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency.

[0041] In one embodiment, an implementation process of the present invention is as follows:

[0042] Step 1: Collecting a data on the output frequency f(T)—the corresponding compensation voltage V.sub.c(T)

[0043] At the room temperature, inputting a compensation voltage to the voltage control terminal of the VCXO 1, so that the output frequency of the VCXO 1 is the target frequency f.sub.0. On this basis, collecting the output frequency f(T) of the VCXO 1, when the temperature is T, adjusting the compensation voltage V.sub.c(T) to make the output frequency of the VCXO 1 changed to the target frequency f.sub.0, recording the value of the compensation voltage V.sub.c(T); changing the ambient temperature T continuously, repeating aforementioned steps to obtain the data on the output frequency f(T)—the corresponding compensation voltage V.sub.c(T).

[0044] Step 2: Constructing a binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled

[0045] Converting the values of the output frequency f(T) and the corresponding compensation voltage V.sub.c(T) obtained from step 1 into binary codes to construct the binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled, and storing the binary coding table into the microprocessor 5.

[0046] Step 3: Obtaining the compensation voltage value and convert it into the corresponding analog voltage signal

[0047] Finding a compensation voltage value in the binary coding table according to the frequency value sent by the analog-to-digital converter 4, and sending it to the digital-to-analog converter 201 and converting it into a corresponding analog voltage signal.

[0048] Step 4: Modulating and filtering the analog voltage signal converted in step 3 through the signal conditioning circuit 202 and the filter 203 to obtain a compensation voltage V.sub.c(T), and sending the compensation voltage V.sub.c(T) to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency f.sub.0.

[0049] FIG. 3 is a diagram of an acquisition system for obtaining a binary coding table, in which the relation of a plurality of frequency values and their respective corresponding compensation voltage values are filled.

[0050] In one embodiment, an acquisition system shown in FIG. 3 is employed to obtain a binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled.

[0051] An implementation process as follows is employed to realize the TCXO based on digital circuit:

[0052] Step 1: using an acquisition system shown in FIG. 3 to collect and construct a binary coding table of the TCXO, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled.

[0053] Placing a TCXO of the present invention into the high and low temperature test box. When the high and low temperature test box is at a certain temperature T, the output frequency f(T) of the TCXO is converted into a binary code by a frequency meter and sent to a host computer, the host computer controls a programmable DC regulated power supply to change the voltage of the voltage control terminal of the VCXO 1, so that the output frequency of the VCXO 1 is the target frequency Jo then recording the value of the compensation voltage V.sub.c(T), and converting it into a binary code; Changing the ambient temperature T continuously, repeating aforementioned steps to obtain a binary coding table, in which a plurality of frequency values and their respective corresponding compensation voltage values are filled, and storing the binary coding table into the microprocessor 5.

[0054] Step 2: disconnecting the acquisition system used in step 1, i.e. just placing the TCXO of the present invention into the high and low temperature test box, where the power divider divides the signal with desired frequency into two signals, one is used as the output of the TCXO and the other as input is sent to the analog-to-digital converter, the analog-to-digital converter converts the signal with desired frequency into a corresponding frequency value with binary form, and sends the frequency value to the microprocessor, the microprocessor finds a compensation voltage value in the binary coding table which is obtained through step 1, the compensation voltage value is sent to a digital-to-analog converter converting it into a corresponding analog voltage signal; modulating and filtering the analog voltage signal through the signal conditioning circuit and the filter to obtain a compensation voltage V.sub.c(T), and sending the compensation voltage V.sub.c(T) to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency f.sub.0.

[0055] Step 3: changing the temperature of the high and low temperature test box, and repeating step 2, a real-time temperature compensation of the TCXO can be achieved under different temperatures. According to the test, the temperature is well be compensated in present invention.

[0056] According to the above description, it is understood that the essence of the present invention is that the output frequency f(T) of the TCXO to be compensated is directly connected with the compensation voltage V.sub.c(T) in real time, and the compensation voltage is fed back to the voltage control terminal of the VCXO to be compensated to compensate, so that the output frequency after compensation is equal to the target frequency signal, thus the purpose of temperature compensation is achieved.

[0057] While illustrative embodiments of the invention have been described above, it is, of course, understand that various modifications will be apparent to those of ordinary skill in the art. Such modifications are within the spirit and scope of the invention, which is limited and defined only by the appended claims.