CN113517938A - Automatic calibration system for transceiver - Google Patents
Automatic calibration system for transceiver Download PDFInfo
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- CN113517938A CN113517938A CN202111068208.3A CN202111068208A CN113517938A CN 113517938 A CN113517938 A CN 113517938A CN 202111068208 A CN202111068208 A CN 202111068208A CN 113517938 A CN113517938 A CN 113517938A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/20—Monitoring; Testing of receivers
- H04B17/21—Monitoring; Testing of receivers for calibration; for correcting measurements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/10—Monitoring; Testing of transmitters
- H04B17/11—Monitoring; Testing of transmitters for calibration
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/10—Monitoring; Testing of transmitters
- H04B17/11—Monitoring; Testing of transmitters for calibration
- H04B17/13—Monitoring; Testing of transmitters for calibration of power amplifiers, e.g. gain or non-linearity
Abstract
The invention discloses an automatic calibration system for a transceiver, wherein a receiving part of the automatic calibration system comprises an adjustable low-noise amplifier connected to a degree calibration module through a mixer, an amplitude calibration module is connected to a variable gain amplifier through an adjustable low-pass filter, and the variable gain amplifier is connected to a baseband through an analog-digital converter; the transmitting part comprises an adjustable power amplifier, a baseband is connected to a digital-to-analog converter, the digital-to-analog converter is connected to the adjustable gain amplifier through an adjustable low-pass filter, the adjustable gain amplifier is connected to the adjustable power amplifier through a mixer, a phase-locked loop is connected with a digital compensation crystal oscillator and a voltage-controlled oscillator, an IQ amplitude and phase mismatch calibration circuit comprises a switch S1, a switch S2, an inverter and a capacitor, the digital compensation crystal oscillator is connected to the inverter through a switch S1, the inverter is connected to one end of a coupling capacitor through a switch S2, and the other end of the coupling capacitor is connected to the input end of the low-noise amplifier.
Description
Technical Field
The present invention relates to the field of communications, and more particularly to an automatic calibration system for image rejection and carrier leakage problems caused by amplitude, phase and dc mismatch between in-phase/quadrature (IQ) signals in a radio transceiver.
Background
In a radio direct-conversion transceiver structure, the performance of received and transmitted signals can be seriously affected by IQ amplitude and phase mismatch, and carrier leakage can be caused by direct-current mismatch during transmission, so that the signal-to-noise ratio of the transmitted signal and the accurate control of the transmission power are seriously affected. IQ amplitude, phase and dc mismatch calibration become important components in direct conversion transceivers.
In the existing IQ amplitude and phase mismatch calibration, a test signal is added to an input end of an LNA, and IQ mismatch evaluation calculation is performed on IQ data acquired by an ADC through a receiving channel, so that IQ mismatch is minimized by controlling an RF corresponding register, thereby implementing calibration of IQ mismatch, as shown in fig. 1. The calibration method needs a signal source and a special test platform, the cost is high, and due to the change of the process and the temperature, the values of IQ mismatch registers of different chips in different working environments are not completely the same, so the IQ mismatch correction method has obvious limitation.
In addition, in the existing transmission direct current mismatch, a test instrument needs to be externally connected to the PA end, the baseband sends an IQ direct current signal with 0 amplitude, the radio frequency power amplifier outputs a leakage signal of a carrier due to the IQ direct current mismatch, the external test instrument measures the output power of the carrier leakage signal, and a corresponding RF direct current offset correction register is adjusted to minimize the output power of the carrier, so that the calibration of direct current offset is realized, as shown in fig. 2. The calibration method also needs to be externally connected with a test instrument and a test platform, and has the problems of high consumption and complex operation.
Disclosure of Invention
The invention aims to provide an automatic calibration system for a transceiver, which has the advantages that IQ amplitude, phase and direct current mismatch of the transceiver after power-on can be automatically calibrated without an external test instrument and a test platform, so that the calibration cost is reduced, and the calibration efficiency is improved.
The purpose of the invention is mainly realized by the following technical scheme:
an automatic calibration system for a transceiver includes a receiving section, a transmitting section, a baseband, a phase locked loop; the receiving part comprises an adjustable low noise amplifier, the adjustable low noise amplifier is connected to the input end of the degree calibration module through a mixer, the output end of the amplitude calibration module is connected to the input end of the variable gain amplifier through an adjustable low pass filter, and the output end of the variable gain amplifier is connected to a baseband through an analog-digital converter; the transmitting part comprises an adjustable power amplifier, a baseband is connected to the input end of a digital-to-analog converter, the output end of the digital-to-analog converter is connected to the input end of the adjustable gain amplifier through the input end of an adjustable low-pass filter, the output end of the adjustable gain amplifier is connected to the input end of the adjustable power amplifier through a mixer, the input end of a phase-locked loop is connected with the output end of a digital compensation crystal oscillator, the output end of the phase-locked loop is connected to the input end of a voltage-controlled oscillator, the output end of the voltage-controlled oscillator is connected to a phase calibration module, the phase calibration module outputs quadrature signals to the mixer of the receiving part and the mixer of the transmitting part, an IQ amplitude and phase mismatch calibration core circuit comprises a switch S1, a switch S2, an inverter and a capacitor, the output end of the digital compensation crystal oscillator is connected to the input end of the inverter through a switch S1, the output of the inverter is connected via a switch S2 to one end of a coupling capacitor, the other end of which is connected to the input of the adjustable low noise amplifier of the receiving part.
As a preferred technical scheme, the IQ direct current mismatch calibration core circuit comprises an RF detection circuit, a low-speed analog-digital converter and a direct current offset calibration module. The input end of the direct current offset calibration module is connected with the baseband, and the output end of the direct current offset calibration module outputs a signal to one of the mixers of the sending part. The input end of the RF detection circuit is connected with the output end of the adjustable power amplifier, the output end of the RF detection circuit is connected to the input end of the low-speed analog-digital converter, and the output end of the low-speed analog-digital converter is connected to the baseband through the SPI interface.
As a preferred solution, the inverter is a small-sized inverter.
As a preferred technical scheme, the coupling capacitor is a small-size coupling capacitor.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a block diagram of a conventional IQ amplitude and phase mismatch calibration system;
FIG. 2 is a schematic diagram of an IQ DC mismatch calibration structure of the prior art;
fig. 3 is a circuit schematic of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Examples
An automatic calibration system for a transceiver includes a receiving section, a transmitting section, and a baseband.
The receiving part comprises a tunable Low Noise Amplifier (LNA), signals enter the system through the tunable low noise amplifier, the output of the tunable low noise amplifier is divided into two paths which are respectively connected with the input end of a Mixer (MIX), the output ends of the two paths of mixers are respectively connected with the input end of an amplitude calibration module, the output end of the amplitude calibration module is connected with the input end of a tunable Low Pass Filter (LPF), the output end of the tunable low pass filter is connected with the input end of a Variable Gain Amplifier (VGA), the output end of the variable gain amplifier is connected with the input end of an analog-to-digital converter (ADC), and the output end of the analog-to-digital converter is connected with a baseband.
The transmitting part comprises an adjustable Power Amplifier (PA), a baseband is connected to input ends (DAC) of two paths of digital-to-analog converters, output ends of the two paths of digital-to-analog converters are respectively connected to input ends of adjustable low-pass filters, output ends of the adjustable low-pass filters are connected with input ends of adjustable gain amplifiers, output ends of the adjustable gain amplifiers are respectively connected with input ends of mixers, and output ends of the mixers are respectively connected to input ends of the adjustable power amplifiers and used for outputting signals.
The automatic calibration system further comprises a Phase Locked Loop (PLL), wherein the input end of the PLL is connected with the output end of a digital compensated crystal oscillator (DCXO), the output end of the PLL is connected with the input end of a Voltage Controlled Oscillator (VCO), the output end of the VCO is connected with a phase calibration module, and the phase calibration module outputs quadrature signals to the mixer of the receiving part and the mixer of the transmitting part.
As shown in fig. 3, in the present embodiment, the IQ amplitude and phase mismatch calibration core circuit includes a switch S1, a switch S2, an inverter, and a capacitor. The output terminal of the digital compensated crystal oscillator is connected to the input terminal of the inverter through a switch S1, the output terminal of the inverter is connected to one terminal of the coupling capacitor through a switch S2, and the other terminal of the coupling capacitor is connected to the input terminal of the adjustable low noise amplifier of the receiving part. The inverter is a small-sized inverter, and the coupling capacitor is a small-sized coupling capacitor.
The working principle of the embodiment is that a square wave signal of the crystal oscillator frequency is generated through a small-sized inverter, and then the square wave signal is injected into the input port of the adjustable low-noise amplifier through a small-sized coupling capacitor to be used as an IQ calibration reference input signal. Because the square wave signal of the crystal oscillator frequency contains each subharmonic component, the harmonic signal closest to the receiving RF frequency can be selected as a reference signal, received by the RF receiving channel, sampled by the analog-digital converter and then sent to the baseband circuit for calibration. Due to IQ amplitude and phase mismatch, the image signal rejection varies as the mismatch varies as the signal passes through the complex filter. The calibration algorithm of the baseband part only needs to filter out useful signals (for example, to filter out signals of a positive frequency part) through a complex filter, reserve image signals to carry out power calculation, and complete calibration by adjusting an RF calibration control word to minimize the power of the image signals. Because the same local oscillator signal is adopted for receiving and transmitting of the RF chip and the same amplitude adjusting channel is shared, the IQ control word after receiving calibration can be directly used for a transmitting channel.
As shown in fig. 3, in the present embodiment, the IQ dc mismatch calibration core circuit includes an RF detection circuit, a low speed analog-to-digital converter, and a dc offset calibration module. The input end of the direct current offset calibration module is connected with the baseband, and the output end of the direct current offset calibration module outputs a signal to one of the mixers of the sending part. The input end of the RF detection circuit is connected with the output end of the adjustable power amplifier, the output end of the RF detection circuit is connected to the input end of the low-speed analog-digital converter, and the output end of the low-speed analog-digital converter is connected to the baseband through the SPI interface.
The working principle of this embodiment is as follows: the RF detection circuit and the low-speed analog-digital converter are integrated in a chip to detect the power of carrier leakage and replace the original external frequency spectrograph. When the IQ branch in the transmitting channel has direct current mismatch, the output end of the power amplifier has carrier power output, which is called carrier leakage, and the carrier leakage can be eliminated by calibrating the direct current offset of the transmitting channel. The specific calibration scheme is as follows: the base band sends IQ direct current signals (complement is all 0 signals) with 0 amplitude, the radio frequency power amplifier can output leakage signals of carrier waves at the moment, a power detection circuit of PA output radio frequency signals is added in the RF chip, detection results are converted into digital signals through a low-speed analog-digital converter and sent to a read-only register of the SPI, and the base band can read current power detection results through the SPI. And the baseband controls the direct current offset calibration control word of the RF, so that the calibration is completed when the local oscillator leakage power of the RF detection is minimum.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. An automatic calibration system for a transceiver includes a receiving section, a transmitting section, a baseband, a phase locked loop; the receiving part comprises an adjustable low noise amplifier, the adjustable low noise amplifier is connected to the input end of the degree calibration module through a mixer, the output end of the amplitude calibration module is connected to the input end of the variable gain amplifier through an adjustable low pass filter, and the output end of the variable gain amplifier is connected to a baseband through an analog-digital converter; the transmitting part comprises an adjustable power amplifier, a baseband is connected to the input end of a digital-analog converter, the output end of the digital-analog converter is connected to the input end of the adjustable gain amplifier through the input end of an adjustable low-pass filter, the output end of the adjustable gain amplifier is connected to the input end of the adjustable power amplifier through a mixer, the input end of a phase-locked loop is connected with the output end of a digital compensation crystal oscillator, the output end of the phase-locked loop is connected to the input end of a voltage-controlled oscillator, the output end of the voltage-controlled oscillator is connected to a phase calibration module, the phase calibration module outputs quadrature signals to the mixer of the receiving part and the mixer of the transmitting part, the IQ amplitude and phase mismatch calibration core circuit comprises a switch S1, a switch S2, an inverter and a capacitor, the output end of the digital compensation crystal oscillator is connected to the input end of the inverter through a switch S1, the output of the inverter is connected via a switch S2 to one end of a coupling capacitor, the other end of which is connected to the input of the adjustable low noise amplifier of the receiving part.
2. The automatic calibration system of claim 1, wherein the IQ DC mismatch calibration core circuit comprises an RF detector circuit, a low speed analog-to-digital converter, and a DC offset calibration module, wherein an input of the DC offset calibration module is connected to the baseband, an output of the DC offset calibration module outputs a signal to one of the mixers of the transmitter, an input of the RF detector circuit is connected to an output of the adjustable power amplifier, an output of the RF detector circuit is connected to an input of the low speed analog-to-digital converter, and an output of the low speed analog-to-digital converter is connected to the baseband through the SPI interface.
3. The automatic calibration system of claim 1, wherein the inverter is a small-sized inverter.
4. The automatic calibration system of claim 1, wherein the coupling capacitor is a small-sized coupling capacitor.
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| CN202111068208.3A CN113517938B (en) | 2021-09-13 | 2021-09-13 | Automatic calibration system for transceiver |
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Cited By (1)
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| CN114900200A (en) * | 2022-05-18 | 2022-08-12 | 青岛柯锐思德电子科技有限公司 | UWB receiver front-end data processing method based on digital mixing |
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