WO2013000239A1

WO2013000239A1 - Phase-locked loop, wideband transmitter and carrier leakage calibration method of wideband transmitter

Info

Publication number: WO2013000239A1
Application number: PCT/CN2011/082969
Authority: WO
Inventors: 王珊; 胡小娟; 亓刚; 赵娜
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-06-30
Filing date: 2011-11-25
Publication date: 2013-01-03
Also published as: CN102857221A; CN102857221B

Abstract

Provided are a phase-locked loop, a wideband transmitter and a carrier leakage calibration method of the wideband transmitter. The phase-locked loop comprises a phase discriminator, a loop filter and multiple voltage-controlled oscillators. The phase discriminator outputs a signal to the loop filter, and the loop filter selectively outputs a signal to any of the multiple voltage-controlled oscillators. The frequency output range of the transmitter is increased, unlock of the phase-locked loop caused by environmental changes is prevented, the reliability of operation of the transmitter is improved, and the validity and reliability of carrier leakage calibration data of the wideband transmitter are ensured.

Description

Carrier leakage calibration method for phase locked loop, wideband transmitter and wideband transmitter

Technical field

The present invention relates to the field of mobile communication technologies, and in particular, to a carrier leakage calibration method for a phase locked loop, a wideband transmitter, and a wideband transmitter.

Background technique

In the field of mobile communications, transmitters are used in Global System For Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access (CDMA) and long-term applications. In a variety of mobile communication systems, such as the Long Term Evolution (LTE), the working process of the transmitter is as follows: First, the digital signal from the baseband is converted into an analog baseband signal;

Then, filtering and up-converting the signal is completed;

Finally, the RF signal is converted by the RF power amplifier through the antenna. In the field of mobile communications, although the technology of the transmitter is relatively mature, it can only work in a single frequency band and mode, with relatively few functions, insufficient flexibility, and limited scalability. In addition, in the frequency conversion process, some unwanted signals, such as local oscillator leakage signals and sideband signals, are inevitable. These unwanted signals may affect the subsequent power amplifier circuit of the transmitter, causing the transmitter spectrum transmission to not meet the requirements of the protocol standard. In addition, when the carrier leakage signal and the transmission signal enter the power amplifier at the same time, the intermodulation between them deteriorates due to the nonlinearity of the power amplifier. , may affect the digital pre-distortion effect.

Summary of the invention

The technical problem to be solved by the present invention is to provide a carrier leakage calibration method for a phase locked loop, a wideband transmitter and a wideband transmitter, which can improve the frequency output range of the transmitter.

In order to solve the above technical problem, the present invention provides a phase locked loop, which includes: a phase detector, a loop And a plurality of voltage controlled oscillators, wherein the phase detector outputs a signal to the loop filter, and the loop filter selectively outputs a signal to any one of the plurality of voltage controlled oscillators. The phase locked loop of the present invention may further comprise at least one variable reactance component, each of which is connected to the plurality of voltage controlled oscillators. The phase locked loop of the present invention may further include one or more frequency dividers connected to the output of the voltage controlled oscillator to provide a divided output signal. The phase locked loop of the present invention is in a plurality of voltage controlled oscillators in which adjacent voltage controlled oscillators have overlapping frequencies within a required operating temperature range. The present invention also provides a wideband transmitter, comprising: an IQ modulator and a phase-locked loop, the phase-locked loop is connected to the IQ modulator to provide a local oscillator signal for the IQ modulator, wherein the phase-locked loop comprises: a phase detector, A loop filter and a plurality of voltage controlled oscillators, wherein the phase detector outputs a signal to the loop filter, and the loop filter selectively outputs a signal to any one of the plurality of voltage controlled oscillators. The phase locked loop in the wideband transmitter of the present invention may further include at least one variable reactance component, each of which is connected to the plurality of voltage controlled oscillators. The phase locked loop in the wideband transmitter of the present invention may also include one or more frequency dividers coupled to the output of the voltage controlled oscillator to provide a divided output signal. In the phase locked loop of the wideband transmitter of the present invention, in a plurality of voltage controlled oscillators, adjacent voltage controlled oscillators have overlapping frequencies within a required operating temperature range. The present invention also provides a carrier leakage calibration method for a wideband transmitter, which is applied to a wideband transmitter including a plurality of voltage controlled oscillators, including:

Calculate the frequency range of the adjacent voltage controlled oscillators in the multiple voltage controlled oscillators, and determine whether the calibration frequency points are in the overlapping frequency range. If yes, specify one for the calibration frequency points from the adjacent voltage controlled oscillators. The voltage controlled oscillator is locked; after a voltage controlled oscillator lock is specified for the calibration frequency point, the local oscillator signal is provided for the broadband modulator's IQ modulator, and the carrier leakage calibration of the IQ modulator is completed by adjusting the baseband DC component. And save the calibration data. In the carrier leakage calibration method of the present invention, a voltage controlled oscillator lock can be specified for the calibration frequency point. Includes:

Calculate the judgment threshold according to the locked upper limit frequency and the lock lower limit frequency of the adjacent voltage controlled oscillator; compare the calibration frequency point with the judgment threshold, and if the calibration frequency point is smaller than the judgment threshold, specify the lock in the adjacent voltage controlled oscillator The voltage controlled oscillator with a lower limit frequency is locked; if the calibration frequency is greater than the judgment threshold, the voltage controlled oscillator with a larger upper limit frequency in the adjacent voltage controlled oscillator is designated to be locked. The carrier leakage calibration method of the present invention may further include:

Before calculating the frequency range in which the adjacent voltage controlled oscillators overlap in the plurality of voltage controlled oscillators, the frequency coverage of the plurality of voltage controlled oscillators needs to be determined; when the calibration frequency points are not in the overlapping frequency range, according to the multiple The frequency coverage of the voltage controlled oscillator specifies a voltage controlled oscillator lock for the calibration frequency. The carrier leakage calibration method of the present invention may further include:

After the voltage controlled oscillator is locked for the calibration frequency point, the number of the voltage controlled oscillator is recorded. When the set frequency point command is received, it is judged whether the set frequency point is in the overlapping frequency range, and if so, according to the voltage controlled oscillation The number of the device, call the corresponding voltage controlled oscillator, and enable the corresponding calibration data.

In summary, the wideband transmitter supported by the wideband phase locked loop (PLL) proposed by the present invention can work in multiple modes to adapt to the development of communication technologies and the needs of suppliers. BRIEF abstract

1 is a block diagram of a wideband transmitter system according to an embodiment of the present invention;

Figure 2 is a diagram showing the working process of a conventional phase-locked loop;

3 is a working process diagram of a broadband phase locked loop according to an embodiment of the present invention;

4 is a working process diagram of an IQ modulator according to an embodiment of the present invention;

FIG. 5 is a flowchart of a carrier leakage calibration of a broadband transmitter according to an embodiment of the present invention; FIG.

FIG. 6 is a flowchart of a carrier leakage enable calibration data of a broadband transmitter according to an embodiment of the present invention. Preferred embodiment of the invention

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the features in the embodiments and the embodiments in the present application may be arbitrarily combined with each other.

FIG. 1 shows a broadband transmitter supporting multiple standards according to an embodiment of the present invention, including: a high-sample rate IQ two-way digital-to-analog converter (DAC), and an IQ two-way low-pass filter ( Low Pass Filter (LPF), Phase Locked Loop (PLL), Wideband RF IQ Modulator, Digital Variable Gain Amplifier (DVGA) and Power Amplifier (Power Amplifier) PA) six parts. The salient feature of the embodiments of the present invention is that a broadband phase-locked loop is used to provide a broadband local oscillator signal to the IQ modulator through a wideband phase-locked loop to implement a wideband transmitter.

2 is a structure of a conventional narrow-band phase-locked loop, and FIG. 3 is a structure of a wide-band phase-locked loop according to an embodiment of the present invention. The phase-locked loop is a closed-loop phase error control system that compares an input signal with a voltage-controlled oscillator output signal. The phase difference produces an error control voltage to adjust the frequency of the voltage controlled oscillator to achieve the same frequency as the input signal.

Embodiments of the present invention integrate multiple voltage controlled oscillators in a phase locked loop

Controlled Oscillator, VCO) to achieve wideband tuning, the working principle of the wideband phase-locked loop is the same as that of the narrow-band phase-locked loop. It compares the phase difference between the input signal and the output signal of the voltage-controlled oscillator, and generates an error control voltage to adjust the voltage control. The frequency of the oscillator, the maximum difference between the wideband phase locked loop and the existing narrowband phase locked loop in the embodiment of the present invention is that the tuning range of the VCO is different. The tuning range of the wideband VCO is based on the following three points:

(1) A conventional phase-locked loop circuit internally contains only one VCO, and the wideband phase-locked loop of the embodiment of the present invention integrates multiple VCO tunings. In the phase-locking process, an appropriate VCO lock can be selected among multiple VCOs. , Broadband tuning through multiple VCO stitching. Since the VCO coverage band will change with high and low temperature and the processing process up and down, in the multi-VCO integration, the frequency overlap range between the two VCOs at room temperature should have sufficient margin to ensure that the wideband PLL is locked in the full temperature range of the full temperature range.

(b) The phase locked loop contains at least one variable component (shown in the figure), and the reactance of the variable component is generally a function of the voltage level. Embodiments of the present invention include a set of variable components, each of which can be coupled to any of the set of reactive components for broadband tuning. (3) The conventional phase-locked loop is a direct output of the voltage-controlled oscillator. In the embodiment of the present invention, the final stage of the wide-band phase-locked loop includes a set of optional frequency dividers, which can directly output the voltage-controlled oscillator or can be divided by two. , after the four-way, etc. output. By combining the above multiple VCOs, the variable component tuning and the output optional divider can achieve a wideband output of VCO from a few hundred megabytes to several Gigabytes. The embodiment of the invention also solves the problem that the carrier leakage calibration fails when the broadband phase locked loop is locked by different VCOs. 4 is a schematic diagram of the working principle of the IQ modulator according to an embodiment of the present invention. If the IQ baseband signal and the local oscillator signal input by the modulator are both ideal sine waves and have no amplitude phase distortion, the output is converted into an ideal single sideband by the modulator. There is no carrier leakage in the signal. However, in practical applications, both the IQ baseband signal and the local oscillator signal through the phase shifter have amplitude and phase distortion, which causes the use of the carrier leakage signal in the modulator output. In the broadband transmitter application, the carrier leakage must be calibrated and suppressed to reach the system. Spurious indicator requirements. The modulator input I, Q and local oscillator signals are expressed by the following formula, where 4 ^ represents the baseband amplitude, 4 is not equal to the Λ baseband amplitude imbalance, % represents the baseband phase, is not equal to the baseband phase imbalance, and A represents the baseband DC component, representing LO amplitude, ^C i is not equal to ^C 2LO amplitude imbalance, ^θ ^ represents LO phase, not equal to LO phase imbalance, and AA represents LO DC component.

I(t) = A _l cos(wt +φ _ι ) + Β _ι

Q{t) = A ύ {wt + φ ₂ ) + B ₂

f _LO _I(t) = C _l cos(w _c t + 0 _l ) + D _l

f _L oQ(t) = C ₂ sin(w _c t + 0 ₂ ) + D ₂ modulator output:

f ₀ (t) = I(t)xf _L0 _I(t) + Q(t)xf _L0 _Q(t)

= [4 cos(wt + ^ ₁ ) + 5 ₁ ]x[C ₁ cos(w _c t + +

+ sm(wt + φ ₂ ) + Β ₂ ]χ[0 ₂ sin(w _c t + 0 ₂ ) + D ₂ ]

= ^cosf^ + w)t + (θ _ι +φ _ι )]+ ² ^ ² cos[(w _c +Αν)ί + (θ ₂ +φ ₂ )]

_C A C

+— -cos[(w _c -w)t + (0 _l -φ^]—— ^-cos[(w _c -w)t + (0 ₂ -φ ₂ )]

+ B _X C _X cos(w _c t + ) + B ₂ C ₂ sin(w _c t + θ ₂ )

+ _{λ λ} Ό _λ cos(wt + φ _χ ) + AJ^ sin(wt + φ ₂ ) + B _X D _X + B ₂ D ₂ where the carrier leakage is: ∞ ^W J + ^J + θ,)

=5^! cos(w _c t + 0 _l ) -B ₂ C ₂ cos(w _c t + θ ₂ +^) It can be seen from the equation that the carrier leakage is not balanced with the amplitude of the DC component of the baseband and the local oscillator signal. ø _ ø ₌

Relatedly, when AG = C ₂ , ^{1 2} 2, the carrier leakage is minimal, and the carrier leakage calibration process adjusts the baseband DC component so that the baseband DC offset is equal to the LO amplitude product = (: ₂ , the carrier leakage amplitude is the smallest. In the conventional PLL Since there is only one VCO, the VCO gain is fixed, the amplitude is unbalanced, and the carrier leakage is only related to the baseband DC offset. However, in the wideband PLL design, since multiple VCOs are integrated internally, in order to ensure that the wideband VCO effectively covers the entire frequency band, the VCO The frequency overlap range is relatively wide, which will cause the frequency points in the overlap region to be randomly locked on the two VCOs, which makes the carrier leakage calibration difficult. Due to the frequency in the overlap region, along with the lock The phase loop power-on will randomly select any VCO lock in the overlap zone. If the calibrated VCO is different from the enabled VCO, the difference between the VCO gains will cause the local oscillator signal amplitude to change, breaking the baseband DC component during calibration. The relationship between the amplitude and the amplitude products during calibration causes the calibration data to be invalid, and the carrier leakage does not meet the system requirements. The embodiment of the present invention specifies the overlapping region. Select a fixed VCO lock to ensure that the frequency calibration data in the overlap region is always valid, and allocate a VCO to the frequency points in the overlap region to prevent the phase change loop from being locked out due to environmental changes, which affects the normal operation of the transmitter. The problem of the carrier leakage calibration failure in the coverage is given. FIG. 5 is a flow chart of the carrier leakage calibration of the broadband VCO according to an embodiment of the present invention, which includes:

Step 501: The transmitter is powered on, the software is loaded, and the modules are initialized. Step 502: Determine the frequency coverage of each VCO in the wideband PLL. Determine the VCO output maximum and minimum frequencies by connecting the VCO to the two reactive components of the edge to determine the VCO. Frequency coverage. Step 503: Calculate the difference between the VCOn lock upper limit frequency (output maximum frequency) and the VCOn+1 lock lower limit frequency (output minimum frequency), obtain the frequency range in which the two VCOs overlap, and store the flash memory in the broadband transmitter. VCO overlap area table; Step 504: After receiving the command to send the frequency point, determine whether the calibration frequency point is in an overlapping frequency range; and configure the frequency point by the intelligent base station controller (IBSC).

Step 505: If one of the VCO locks is specified in the overlapping frequency range, this step includes the following steps: a: Calculate the lock upper limit frequency of VCOn and the lock lower limit frequency of VCOn+1; b: Calculate the judgment threshold, such as

; c : If the calibration frequency is less than the judgment threshold, the voltage controlled oscillator VCOn with a smaller lock lower limit frequency is locked;

d: If it is greater than the judgment threshold, it is locked with the voltage controlled oscillator VCOn+1 with a large upper limit frequency;

e: Record the number of the VCO that calibrates the frequency lock.

Step 506: If the calibration frequency is not in the overlapping area, search for a VCO that can be locked;

The corresponding VCO is selected by determining which VCO's tuning bandwidth the calibration frequency falls into.

Step 507: After the calibration frequency point is specified to uniquely lock the VCO, the local oscillator signal is provided for the broadband modulator of the wideband transmitter, and the baseband DC component is adjusted by a convenient method of large, medium, and small steps to complete the carrier leakage calibration of the IQ modulator. The carrier leakage calibration is related to the gain of the VCO that calibrates the frequency lock.

Step 508: Save the calibration data to complete the calibration.

宽带 The above process configuration can complete the broadband transmitter carrier leakage calibration, and ensure that the frequency in the overlapping area is not at the edge of the VCO, which can improve the reliability of the transmitter operation.

The embodiment of the present invention further includes a process of enabling calibration data as shown in FIG. 6, and the steps are as follows:

601: transmitter power-on, software loading and initialization of each module;

602: After receiving the set frequency point command, searching for a VCO overlap area table stored in the flash; 603: If the set frequency point is in the overlapping frequency range, the VCO number specified in the flash is called;

604: Search for VCO lock if the set frequency point is not in the overlapping frequency range;

605: Enable calibration data.

The carrier leakage calibration failure problem of multiple VCOs covered by multiple VCOs is solved by the above carrier leakage calibration and enabling process. The optimization algorithm is used to select a fixed VCO lock for the frequency points in the overlap region, which not only avoids the loss of the phase-locked loop when the frequency is configured to the VCO edge, and ensures the validity and reliability of the carrier leakage calibration data.

The modules and steps of the foregoing embodiments of the present invention may be implemented by a general-purpose computing device, which may be centralized on a single computing device or distributed over a network of multiple computing devices. Alternatively, they may Implemented by program code executable by the computing device, such that they may be stored in a storage device by a computing device, or they may be fabricated into individual integrated circuit modules, or a plurality of modules or steps thereof may be fabricated into a single The integrated circuit module is implemented. Thus, embodiments of the invention are not limited to any specific combination of hardware and software.

The above description is only for the embodiments of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Industrial Applicability The broadband transmitter supported by the wideband phase locked loop (PLL) proposed by the embodiment of the present invention can work in various modes to adapt to the development of communication technologies and the needs of suppliers.

Claims

Claim

What is claimed is: 1. A phase locked loop comprising a phase detector, a loop filter and a plurality of voltage controlled oscillators, wherein: the phase detector is configured to output a signal to the loop filter;

The loop filter is configured to selectively output a signal to any of the plurality of voltage controlled oscillators.

2. The phase locked loop of claim 1 wherein said phase locked loop further comprises at least one variable reactance component, said variable reactance component being configured to be coupled to said plurality of voltage controlled oscillators, respectively.

3. The phase locked loop of claim 2, said phase locked loop further comprising one or more frequency dividers, said frequency divider being arranged to be coupled to an output of said voltage controlled oscillator to provide a frequency division After the output signal.

4. The phase locked loop of claim 1 wherein, in said plurality of voltage controlled oscillators, adjacent voltage controlled oscillators are arranged to have overlapping frequencies within a desired operating temperature range.

5. A wideband transmitter comprising an IQ modulator and a phase locked loop, the phase locked loop being coupled to the IQ modulator to provide a local oscillator signal to the IQ modulator, wherein:

The phase locked loop includes a phase detector, a loop filter and a plurality of voltage controlled oscillators, wherein: the phase detector is configured to output a signal to the loop filter, and the loop filter is set to be Optionally outputting a signal to any of the plurality of voltage controlled oscillators.

The wideband transmitter according to claim 5, wherein the phase locked loop further comprises at least one variable reactance component, and the variable reactance component and the plurality of voltage controlled oscillators are respectively connected.

7. The wideband transmitter of claim 6, wherein the phase locked loop further comprises one or more frequency dividers, the frequency divider being configured to be coupled to an output of the voltage controlled oscillator, provided The divided output signal.

8. The wideband transmitter of claim 5, wherein among the plurality of voltage controlled oscillators, adjacent voltage controlled oscillators are arranged to have overlapping frequencies within a required operating temperature range.

9. A carrier leakage calibration method for a wideband transmitter for use in a wideband transmitter comprising a plurality of voltage controlled oscillators, the carrier leakage calibration method comprising:

Calculating a frequency range in which the adjacent voltage controlled oscillators overlap in the plurality of voltage controlled oscillators, determining whether the calibration frequency point is in the overlapping frequency range, and if so, from the adjacent voltage controlled oscillator The calibration frequency point specifies a voltage controlled oscillator lock;

After the step of assigning a voltage controlled oscillator lock to the calibration frequency point, providing a local oscillator signal for the IQ modulator of the wideband transmitter, and completing the carrier of the IQ modulator by adjusting the baseband DC component Leak calibration and save calibration data.

10. The method of claim 9, wherein the step of assigning a voltage controlled oscillator lock to the calibration frequency point comprises:

Calculating a judgment threshold according to a locked upper limit frequency and a lock lower limit frequency of the adjacent voltage controlled oscillator; comparing the calibration frequency point with the determination threshold value, if the calibration frequency point is smaller than the determination threshold value, specifying The voltage-controlled oscillator with a lower locking lower limit frequency in the adjacent voltage-controlled oscillator is locked; if the calibration frequency point is greater than the determination threshold, the voltage-controlled oscillation of the upper limit frequency of the adjacent voltage-controlled oscillator is specified. Locked.

11. The method of claim 9, the carrier leakage calibration method further comprising: determining the plurality of voltage ranges before the step of calculating a frequency range in which the adjacent voltage controlled oscillators overlap in the plurality of voltage controlled oscillators Frequency coverage of the voltage controlled oscillator; after determining whether the calibration frequency point is in the overlapping frequency range, if not, according to the frequency coverage of the plurality of voltage controlled oscillators, the calibration frequency point Specifies a voltage controlled oscillator lock.

12. The method of claim 10, the carrier leakage calibration method further comprising: providing a local oscillator signal to the IQ modulator of the wideband transmitter after the voltage controlled oscillator is locked for the calibration frequency point Recording the number of the voltage controlled oscillator;

When receiving the set frequency point command, determining whether the set frequency point is in the overlapping frequency range, if yes, calling the corresponding voltage controlled oscillator according to the number of the voltage controlled oscillator, and enabling the corresponding Calibration data.