TEMPERATURE-COMPENSATED CRYSTAL OSCILLATOR BASED ON ANALOG CIRCUIT

Abstract

Disclosed is a temperature-compensated crystal oscillator based on analog circuit; a closed-loop compensation architecture determines the temperature compensation of a crystal oscillator. The power splitter divides the VCXO's current output signal with frequency f=f.sub.0+Δf into two signals, one signal to output of the TCXO and the other signal is sent to an analog frequency-voltage conversion circuit. According to the frequency of the VCXO's current output signal, the analog frequency-voltage conversion circuit produces a voltage signal V(T), which corresponds to current ambient temperature. The difference between V(T) and a reference voltage signal V.sub.ref is produced and amplified to obtain a compensation voltage signal ΔV through a voltage matching circuit. ΔV is smoothed by a filter, then sent to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency f.sub.0, to compensate the frequency of the VCXO's output signal when the ambient temperature is changed.

Claims

1. A temperature-compensated crystal oscillator based on analog circuit, comprising: a VCXO for generating a signal with desired frequency f.sub.0; wherein further comprising: a power splitter for dividing the VCXO's current output signal with frequency f=f.sub.0+Δf into two signals, where one signal is used as the output of the TCXO, the other signal is taken as a frequency-voltage conversion signal; an analog frequency-voltage conversion circuit for receiving the frequency-voltage conversion signal, and converting it, i.e. the VCXO's current output signal with frequency f=f.sub.0+Δf into a voltage signal V(T), which is proportional to the frequency f; a voltage matching circuit for receiving the voltage signal V(T), then producing the difference between the voltage signal V(T) and a reference voltage signal V.sub.ref, i.e. V.sub.ref−V(T), and amplifying the difference to obtain a compensation voltage signal ΔV; where the reference voltage signal V.sub.ref is the voltage signal converted by the frequency-voltage conversion circuit, when the VCXO is at room temperature 25° C., and generates a signal with desired frequency f.sub.0 by adjusting the control voltage of the VCXO; a filter for smoothing the compensation voltage signal ΔV, where the smoothed compensation voltage signal ΔV is sent to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency f.sub.0.

2. A temperature-compensated crystal oscillator based on analog circuit of claim 1, wherein further comprising an adder for adding the filtered compensation voltage signal ΔV to the control voltage VC.sub.0, and obtaining the control voltage VC=VC.sub.0+ΔV; where the control voltage VC is applied to the voltage control terminal of the VCXO to make the VCXO generate a stable signal with desired frequency f.sub.0, so that the frequency of the VCXO's output signal is compensated, when the ambient temperature is changed.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0031] 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:

[0032] FIG. 1 is a diagram of a TCXO based on a thermistor compensation network in prior art;

[0033] FIG. 2 is a diagram of a TCXO based on analog circuit according to one embodiment of the present invention;

[0034] FIG. 3 is a diagram of the TCXO shown in FIG. 2 according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0035] 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.

[0036] FIG. 2 is a diagram of a TCXO based on analog circuit according to one embodiment of the present invention.

[0037] In one embodiment, as shown in FIG. 2, the TCXO based on analog circuit comprises a voltage controlled crystal oscillator, i.e. VCXO 1, a power splitter 2, an analog frequency-voltage conversion circuit 3, a voltage matching circuit 4 and a filter 5.

[0038] The power splitter 2 divides the VCXO's current output signal with frequency f=f.sub.0+Δf into two signals, one signal is used as the output of the TCXO, the other signal is taken as a frequency-voltage conversion signal and sent to the analog frequency-voltage conversion circuit 3, where the Δf is the frequency shift of the crystal resonator in the VCXO 1, which is caused by ambient temperature's change.

[0039] The analog frequency-voltage conversion circuit 3 receives the frequency-voltage conversion signal, and converts it, i.e. the VCXO's current output signal with frequency f=f.sub.0+Δf into a voltage signal V(T), which is proportional to the frequency f, then sends the voltage signal V(T) to the voltage matching circuit 4.

[0040] The voltage matching circuit 4 receives the voltage signal V(T), then produces the difference between the voltage signal V(T) and a reference voltage signal V.sub.ref, i.e. V.sub.ref−V(T), and amplifies the difference to obtain a compensation voltage signal ΔV. Where the reference voltage signal V.sub.ref is the voltage signal converted by the frequency-voltage conversion circuit 3, when the VCXO 1 is at room temperature 25° C., and generates a signal with desired frequency f.sub.0 by adjusting the control voltage of the VCXO 1.

[0041] The filter 5 smoothes the compensation voltage signal ΔV, where the smoothed compensation voltage signal ΔV is sent to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency f.sub.0.

[0042] FIG. 3 is a diagram of the TCXO shown in FIG. 2 according to one embodiment of the present invention.

[0043] In one embodiment, as shown in FIG. 3, the TCXO 1 based on analog circuit further comprises an adder 6 for adding the filtered compensation voltage signal ΔV to the control voltage VC.sub.0, and obtaining the control voltage VC=VC.sub.0+ΔV. The control voltage VC is applied to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency f.sub.0, so that the frequency of the VCXO's output signal is compensated, when the ambient temperature is changed.

[0044] In a process of implementing the present invention, the VCXO 1 generates a signal with desired frequency f.sub.0 by adjusting the control voltage of the VCXO 1 at room temperature 25° C., then, the signal with desired frequency f.sub.0 is sent to the frequency-voltage conversion circuit 3 and converted into a voltage signal. The converted voltage signal is taken as the reference voltage signal V.sub.ref of the voltage matching circuit 4.

[0045] When the TCXO based on analog circuit is in operation at temperature T, the VCXO 1 generates an output signal with frequency f.sub.0+Δf under the control voltage VC.sub.0, which is caused by ambient temperature's change, i.e. the frequency of the VCXO's current output signal is f=f.sub.0+Δf. the VCXO's current output signal is divided into two signals, one signal is used as the output of the TCXO, the other signal is taken as a frequency-voltage conversion signal and sent to the analog frequency-voltage conversion circuit 3.

[0046] The analog frequency-voltage conversion circuit 3 receives the frequency-voltage conversion signal, and converts it, i.e. the VCXO's current output signal with frequency f=f.sub.0+Δf into a voltage signal V(T), which is proportional to the frequency f, then sends the voltage signal V(T) to the voltage matching circuit 4. The voltage matching circuit 4 receives the voltage signal V(T), then produces the difference between the voltage signal V(T) and a reference voltage signal V.sub.ref, i.e. V.sub.ref−V(T), and amplifies the difference to obtain a compensation voltage signal ΔV, the compensation voltage signal ΔV is sent to the filter 5.

[0047] The compensation voltage signal ΔV is smoothed by the filter 5, and sent to the adder 6. In the adder 6, the smoothed compensation voltage signal ΔV is added to the control voltage VC.sub.0, and the compensated control voltage VC=VC.sub.0+ΔV is obtained. The control voltage VC is applied to the voltage control terminal of the VCXO 1 to make the VCXO 1 generate a stable signal with desired frequency f.sub.0, so that the frequency of the VCXO's output signal is compensated, when the ambient temperature is changed.

[0048] 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.