This application claims priority to Taiwan Application Serial Number 110139906, filed on Oct. 27, 2021, which is incorporated by reference in its entirety.
The present application relates to an oscillator frequency control, particularly to a method for building an oscillator frequency adjustment lookup table and a related transceiver or a related large-scale integrated circuit.
In the mobile communication specification, the frequency error requirement is higher, e.g., only 0.1 ppm error tolerance. In other words, in order to meet such mobile communication specifications, the crystal oscillator circuit of the corresponding transceiver must be able to use the oscillator to precisely generate the frequency that meets such requirements. However, in order to meet the above specification, the cost of the system factory often increases significantly; therefore, how to obtain similar results at a lower cost has become one of the urgent issues to be solved in the related field.
The application provides a method for building an oscillator frequency adjustment lookup table in a transceiver or a large-scale integrated circuit, wherein the transceiver or the large-scale integrated circuit generates a clock according to a crystal oscillator external to the transceiver for transceiving, and the transceiver includes an adjustable capacitor set coupled to the crystal oscillator, wherein when an equivalent capacitance of the adjustable capacitor set is a reference value, the crystal oscillator has a reference frequency, and when the equivalent capacitance changes in relative to the reference value, the crystal oscillator correspondingly generates a frequency variation relative to the reference frequency, the method including: obtaining the frequency variations corresponding to a first value, a second value and a third value of the equivalent capacitance; performing interpolation according to the first value, the second value and the third value of the equivalent capacitance and the corresponding frequency variations to obtain the frequency variation corresponding to a first sub-value between the first value and the second value of the equivalent capacitance and obtain the frequency variation corresponding to a second sub-value between the second value and the third value of the equivalent capacitance; and storing the first value, the first sub-value, the second value, the second sub-value and the third value of the equivalent capacitance and the corresponding frequency variations in the oscillator frequency adjustment lookup table in a memory cell of the transceiver.
The application provides a transceiver, configured to generate a clock for transceiving according to a crystal oscillator external to the transceiver, the transceiver including: an adjustable capacitor set, coupled to the crystal oscillator, wherein when the equivalent capacitance of the adjustable capacitor set is a reference value, the has a reference frequency, and when the equivalent capacitance changes relative to the reference value, the crystal oscillator correspondingly generates a frequency variation relative to the reference frequency; perform interpolation according to the first value, the second value and the third value of the equivalent capacitance and the corresponding frequency variations to obtain the frequency variation corresponding to a first sub-value between the first value and the second value of the equivalent capacitance having and obtain the frequency variation corresponding to a second sub-value between the second value and the third value of the equivalent capacitance having oscillator frequency adjustment lookup table, the oscillator frequency adjustment lookup table includes the first value, the first sub-value, the second value, the second sub-value and the third value of the equivalent capacitance and the corresponding frequency variations.
The method for building an oscillator frequency adjustment lookup table and a related transceiver of the present application can reduce chip manufacturing cost
Various aspects of the present application can best be understood upon reading the detailed description below and accompanying drawings. It should be noted that the various features in the drawings are not drawn to scale in accordance with standard practice in the art. In fact, the size of some features may be deliberately enlarged or reduced for the purpose of discussion.
The transceiver 100 includes an adjustable capacitor set 102 coupled to the crystal oscillator 200, wherein the adjustable capacitor set 102 includes a first adjustable capacitor CL1 and a second adjustable capacitor CL2, one terminal of the first adjustable capacitor CL1 is coupled to one terminal of the crystal oscillator 200, and another terminal of the first adjustable capacitor CL1 is coupled to the ground; one terminal of the second adjustable capacitor CL2 is coupled to another terminal of the crystal oscillator 200, and another terminal of the second adjustable capacitor CL2 is coupled to the ground. Therefore, the first adjustable capacitor CL1 and the second adjustable capacitor CL2 are equivalently, connected in series with each other through the ground terminal, and the first adjustable capacitor CL1 and the second adjustable capacitor CL2 that are serially connected have an equivalent capacitance C. By adjusting the equivalent capacitance C, the resonant frequency of the crystal oscillator 200 can be changed.
Generally, the equivalent capacitance value C is adjusted before shipping from the factory to reduce the error between the resonant frequency of the crystal oscillator 200 and the target frequency to within the range allowed by the specification. However, in actual use, it is possible that the temperature change may cause the above error to exceed the range allowed by the specification. As shown in
Therefore, the transceiver 100 needs to monitor the resonant frequency of the crystal oscillator 200 dynamically and control the error of the crystal oscillator 200 at any time by adjusting the adjustable capacitance set 102. However, the equivalent capacitance value C and the resonant frequency of the crystal oscillator 200 are not linearly related, so the correspondence between the capacitance C and the resonant frequency of the crystal oscillator 200 must be recorded in an oscillator frequency adjustment lookup table (hereinafter referred to as the lookup table) in the memory cell 106 of the transceiver 100 in order to know how to adjust the adjustable capacitor set 102 to generate the desired frequency change to compensate the above error.
Referring to
However,
Returning to
To simplify the calculation, the present application proposes to use Taylor expansion to simplify the above relationship into a univariate n-degree polynomial related to the equivalent capacitance C, wherein n is a positive integer, i.e., the oscillation frequency f(C)=α0+α1(C−Cα)+α2(C−Cα)2+ . . . +αn(C−Cα)n, where Cαis the expansion point of the polynomial, α0 is the coefficient of the constant term, α1 is the coefficient of the first term, and so on so forth for α2 to αn. Theoretically, the larger the n, the better the curve approximating the curve shown in
In the present embodiment, the transceiver 100 shown in
Next, the computing unit 104 obtains a first univariate quadratic polynomial as the model representing the curve between the first value C1 and the third value C3 according to the first value C1, the second value C2 and the third value C3 and the corresponding frequency variation Δf1, frequency variation Δf2 and frequency variation Δf3. In other words, the first univariate quadratic polynomial is used to approximate the relationship between the crystal oscillator 200 and the equivalent capacitance C within the range between the first value C and the third value C. In this embodiment, the second value C2 is the average of the first value C1 and the third value C3 in order to reduce the complexity of the computation and to obtain better results; however, the present disclosure is not limited thereto; in some embodiments, the distances between the first value C1, the second value C2 and the third value C3 may also be unequal.
Therefore, the frequency variation corresponding to any value of the equivalent capacitance C between the first value C1 and the third value C3 can be obtained immediately by using the first univariate quadratic polynomial without further measurement and the frequency variation can be recorded in the lookup table of the memory unit 106. Thus, most of the measurement time in the process of building the lookup table can be saved.
Similarly, the computing unit 104 can adjust the equivalent capacitance value of the adjustable capacitor group 102 to a fourth value C4 and then perform measurement to obtain the frequency variation Δf4; then it can adjust the equivalent capacitance value of the adjustable capacitor group 102 to a fifth value C5 and then perform measurement to obtain the frequency variation Δf5. Then, the computing unit 104 obtains a second univariate quadratic polynomial as the model representing the curve between the third value C3 and the fifth value C5 according to the third value C3, the fourth value C4 and the fifth value C5 and the corresponding frequency variation Δf3 (that has been measured previously), frequency variation Δf4 and frequency variation Δf5. In other words, the second univariate quadratic polynomial is used to approximate the relationship between the crystal oscillator 200 and the equivalent capacitance C within the range between the third value C3 and the fifth value C5. Thus, the frequency variation corresponding to any value of the equivalent capacitance C between the third value C3 and the fifth value C5 can be obtained immediately by using the second univariate quadratic polynomial without further measurement and the frequency variation can be recorded in the lookup table of the memory unit 106. Thus, most of the measurement time in the process of building the lookup table can be saved.
In this way, computing unit 104 can obtain a third univariate quadratic polynomial as a model for the curve between the fifth value C5 and the seventh value C7; and obtain a fourth univariate quadratic polynomial as a model for the curve between the seventh value C7 and the ninth value C9 to cover the desired range of frequency variation.
The foregoing embodiments are not intended to limit the scope of the present application. In some embodiments, more than four univariate quadratic polynomials can be used to form the curve between the frequency variation Δf1 to the frequency variation Δf9 in
Number | Date | Country | Kind |
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110139906 | Oct 2021 | TW | national |
Number | Name | Date | Kind |
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20200142000 | Wang | May 2020 | A1 |
20230228886 | Yu | Jul 2023 | A1 |
Number | Date | Country | |
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20230131944 A1 | Apr 2023 | US |