KR20020059745A - Calibration of a transmit branch and/or a receive branch of a quadrature transmitter and/or transceiver - Google Patents

Abstract

In the present invention, a method of calibrating a transmission branch of a transmitter is provided. The low frequency components in the high frequency output signal of the transmit branch are measured. The low frequency component is only present when the transmission branch is not calibrated. From the measured low frequency components, a first compensation signal is derived. The first compensation signal is injected into the in-phase branch of the transmission branch. The second compensation signal is derived and injected into the orthogonal branch of the transmission branch. The first and second compensation signals are swept and modified based on the measured low frequency components. From the sweeping, the minimum values of the measured low frequency components are obtained. Thereafter, the first and second compensation signals are continuously set to the minimum values. In addition to the calibration of the transmit branch, the receive branch can be calibrated in the case of a transceiver. In order to calibrate the receive branch, the calibrated transmitter is coupled to the receive branch. Thereafter, the receive branch is calibrated through sweeping and setting of the receiver branch parameters.

Description

Transmitter, Transceiver and Calibration Method {CALIBRATION OF A TRANSMIT BRANCH AND / OR A RECEIVE BRANCH OF A QUADRATURE TRANSMITTER AND / OR TRANSCEIVER}

U.S. Patent 5,793,817 discloses a DC offset reduction in a transmitter. The transmitter has up-converters and an RF power amplifier through which the transmitter output signal is provided to the antenna. The transmitter has a feedback loop. The feedback loop derives a portion of the output signal and distributes the derived signal to a phase related feedback path. Each feedback path has a frequency-down converter. The DC offset at the input of the upconverter is measured when the feedback around a linearization loop is reduced to zero without changing the dc offset generated at the output of the frequency down converter. The subtractor subtracts the measured DC offset from the feedback loop error signal. This DC nulling eliminates the effects of carrier feedthrough of the down-conversion mixer, thereby improving the resulting carrier feedthrough of the transmitter.

Summary of the Invention

It is an object of the present invention to provide a quadrature transmitter or transceiver in which carrier leakage, gain and phase instability are fully compensated.

Another object of the invention is, in the case of a transceiver, to also calibrate the gain of the receiver branch of the transceiver after calibration of the transmission branch.

It is a further object of the present invention to perform this calibration at different power settings of the transmitter when sweeping and setting the transmitter respectively.

According to the present invention, there is provided a method for calibrating a transmission branch of a transmitter, the method comprising:

Measuring a low frequency component in the high frequency output signal of the transmit branch, wherein the low frequency component is present if the transmitter branch is not calibrated;

Derive a first compensation signal from the measured low frequency component, inject the first compensation signal into an in-phase branch of the transmission branch, induce a second compensation signal, and generate the second compensation signal Injecting a signal into an orthogonal branch of the transmission branch;

Sweeping the first and second compensation signals and adapting the first and second induced compensation signals based on the low frequency component;

Obtaining a minimum value from the measured low frequency component from the sweep;

Continuously setting the first and second compensation signals to the minimum value.

Advantageously, said compensation signal is injected behind a transmission filter in each in-phase and quadrature branch of the transmission branch to achieve optimum carrier leakage compensation.

Preferably, when calibrating the transmitter, the different relative signal strengths of the high frequency output signal, the local oscillator signal and the sideband signal that have not yet been calibrated are considered optimal. This relative signal strength will vary depending on the silicon process used to manufacture the transmitter. For sideband signals that are strong for the carrier leakage signal, carrier leakage compensation is done at the maximum output power, and thus gain and phase error compensation is done at an output power level substantially lower than the output level of the expected maximum carrier leakage. For sideband signals that are weak for the carrier leakage signal, carrier leakage compensation is done at an output power level substantially lower than the output level of the expected maximum carrier leakage, so that gain and phase error compensation is done at full power.

In the case of a transceiver comprising a receive branch in addition to the transmit branch, preferably, the method calibrates the receive branch by sweeping the gain setting in the receive branch, and the error during sweeping of the gain in the receive branch. Obtaining an even smaller value of the signal and measuring the error signal by setting the gain at the receive branch to a value corresponding to the much smaller value. In this way the transceiver is fully calibrated after sweeping and setting.

The present invention relates to a transmitter or a transceiver, and more particularly to a calibration of a transmission branch of such a transmitter or transceiver. In the case of a transceiver, in addition to the calibration of the transmission branch, a receive branch may also be calibrated. Such a transmitter or transceiver may operate in the so-called 2.4 GHz ISM band, or may be any other suitable transmitter or transceiver.

1 is a block diagram of a transceiver according to the present invention;

2 shows a first embodiment of a power detector used in a transceiver according to the present invention;

3 shows a second embodiment of a power detector used in a transceiver according to the present invention;

4 shows a third embodiment of a power detector used in a transceiver according to the present invention;

5 is a diagram illustrating local oscillator leak calibration according to the present invention;

6 illustrates local oscillator leakage,

7 (a) to 7 (d) show the sweeping of transmitter parameters for transmitter calibration,

8 (a) to 8 (b) are diagrams for further explaining transmitter calibration,

9 (a) to 9 (c) are diagrams for describing receiver calibration.

Like reference numerals are used to denote like features in the figures.

1 is a block diagram of a transceiver 1 according to the invention. In the given example, the transceiver 1 is a so-called zero IF transceiver, operating in the so-called 2.4 GHz Industrial, Scientific and Medical (ISM) band, transmitting and receiving at the same frequency so that only a single tuned oscillator is required. It is called. The transceiver 1 comprises a receiving branch 2 and a transmitting branch 3. The receive branch 2 comprises a low noise amplifier (LNA) 4 which is coupled to the antenna 5 via a filter 6 and a transmit / receive switch 7. LNA 4 is coupled to a pair of quadrature mixers 8 and 9, which are in-phase and quadrature receive branches, respectively. Through an AC-coupler 10, the mixer 8 is AC coupled to the low pass filter 11. Through the AC coupler 12, the mixer 9 is coupled to the low pass filter 13. According to the invention, the in-phase receive branch is an adjustable amplifier 14 for adjusting the gain of the receive branch 2 and an injector for injecting a DC voltage to compensate for the DC offset. and an orthogonal receive branch has an injector 16 which injects a DC voltage to compensate for the DC offset. Injectors 15 and 16 may be adders. Instead of the adjustable amplifier 14 in the in-phase receive branch, the adjustable amplifier may be included in the quadrature receive branch. Alternatively, in both in-phase and quadrature receive branches, the transmit branch 3 of the transceiver 1 comprises transmit filters 20 and 21. According to the invention, after the transmission filters 20 and 21, the in-phase and quadrature transmission branches comprise respective injectors 22 and 23 for injecting DC voltages for calibrating the transmission branch 2 and also orthogonal. An adjustable amplifier 24 is included in the transmission branch. In place of the adjustable amplifier 24 in the quadrature transmit branch, an adjustable amplifier can be included in the in-phase receive branch. Alternatively, both in-phase and quadrature transmission branches can include an adjustable amplifier. Despite the respective upconverters or mixers 25 and 26 and adder 27, injectors 22 and 23 are coupled to the transmit power amplifiers 28 and 29. The transmit power amplifier 29 is coupled to the transmit / receive switch 7.

The transceiver further comprises means 40 for measuring low frequency components in the high frequency output signal of the transmission branch 3. In the given example, the means 40 comprises a power detector 41, a high pass filter 42 and an AC voltage detector 43. When the transmission branch 3 is fully calibrated, the power detector 41 provides a constant DC signal so that the AC voltage detector 43 does not generate an output signal. When the transmission branch 3 has not yet been calibrated, the power detector 41 provides a varying DC signal, i.e. a low frequency component, so that the AC voltage detector 43 generates an output signal.

The transceiver 1 further includes a voltage controlled oscillator 50 controlled by a phase locked loop (PLL) 51. VCO 50 provides local oscillator signals to respective mixers 8 and 25 in the in-phase receive and transmit branches, and via an adjustable phase shifter 52, provides a phase shift local oscillator signal. To each mixer 9 and 26 in an orthogonal receive and transmit branch. Adjustable phase shifter 52 is adjustable near 90 ° nominal phase shift.

The transceiver 1 further includes a controller 60. The controller 60 includes a processor 61, a nonvolatile memory 62 that stores nonvolatile data such as programs and calibration data, and a RAM 63 that stores volatile data. The controller 60 samples the received and downconverted signals provided by the injectors 15 and 16, and an analog-to-digital converter (ADC) 64 that samples the output signal provided by the AC voltage detector 43. 65 and 66). The controller 60 includes a digital-to-analog converter (DAC) 67 and 68 for providing respective in-phase and quadrature transmission signals to the transmission filters 20 and 21, and the injector 15 and 16 as a control or calibration signal. It further includes digital-to-analog converters 69, 70, 71, 72, 73, 74 and 75, which provide to amplifier 14, injectors 22 and 23, amplifier 24 and phase shifter 52, respectively. In addition, the processor 61 controls a switch 80 that couples the output of the power amplifier 29 to the output of the LNA 4 via an attenuator 81.

2 is a first embodiment of the power detector 41. In this embodiment, the power detector 41 includes an AM demodulator formed by a diode 90, a resistor 91 and a capacitor 92. The AM demodulator provides an output voltage that is proportional to the square root of the RF output power provided by the power amplifier 28.

3 is a second embodiment of the power detector 41. In this embodiment, the power detector 41 includes a micro-strip coupler 93 and a Schottky diode 94. In this embodiment, the power detector provides an output voltage proportional to the RF output power provided by the power amplifier 28.

4 is a third embodiment of the power detector 41. In this embodiment, the power detector 41 includes a mixer 95, a resistor 96 and a capacitor 97. In this embodiment, the power detector provides an output voltage proportional to the RF output power provided by the power amplifier 28.

5 illustrates a local oscillator leak calibration according to the present invention. In a perfectly calibrated transmission branch 3, the calibrated four phase orthogonal signal constellation for carrier leakage, gain, and phase, shown as four points, is a complete circle 100, such as the signal represented by the dotted line. . That is, amplifier 28 provides a constant RF power, represented by a constant radius r. Due to carrier leakage from the VCO 50 through the mixers 25 and 26 in the uncalibrated transmission branch, the signal constellation for the calibrated gain and phase is represented by the solid line 101 with a new center. Is shifted as The shifted circle 101 causes the transmission branch to have different DC components V _{DC_I} and V _{DC_Q} in in-phase and quadrature transmission branches. Since the radius r is no longer constant, the RF power at the amplifier 28 changes significantly in proportion to the square of the radius r. Carrier leakage is compensated for by injecting the appropriate calibration voltage into the injectors 22 and 23. In the case of gain and phase not yet calibrated in the transmission branch 3, the circle adopts the form of an ellipse, so gain and phase calibration is also required.

6 shows local oscillator leakage in the frequency domain. The spectra of f _RF and carrier leakage signal f _LO for a single tone transmit signal are shown.

7 (a) to 7 (d) show the sweeping of transmitter parameters for transmitter calibration. In FIGS. 7A and 7B, the respective sweeps of signals V ₁ and V ₂ to injectors 22 and 23 are shown. DACs 72 and 73 are set to V _{1, opt} and V _{2, opt} , respectively. This compensates for carrier leakage. In order to obtain better calibration, the sweeping and setting of V ₁ and V ₂ are repeated at least once. 7 (c) and 7 (d), the sweeps of the signals ΔG ₁ and Δθ, respectively, to the amplifier 24 and the phase shifter 52 are shown. The DACs 74 and 75 are set at ΔG _{1, opt} and Δθ _{, opt} , respectively. This compensates for gain and phase imbalance in the transmission branch 3.

8 (a) to 8 (b) show calibration of gain and phase imbalance that have not yet been calibrated. Here, as shown in FIG. 8 (a), the sideband signal power P _SB due to uncalibrated gain and phase imbalance is much weaker than the carrier leakage signal power P _LO , both of which are shown for P _RF . It is. It is then desirable to initiate calibration at the signal power at a level below the maximum power equal to the worst case expected LO leakage, which depends on the IC process. As shown by the arrows in Fig. 8A, the first low leakage is compensated. Then, as shown in Fig. 8 (b), the maximum power is applied to the transmission branch 3, resulting in signal powers P ' _SB , P' _LO and P ' _RF . Since P _LO does not change with the power of the transmit signal P ' _LO , the reduced carrier leakage signal does not change even when increasing the transmit power. At maximum power, gain and phase imbalance are calibrated to reduce sideband power. For better results, the calibration is repeated at least once.

For a much stronger transmission signal compared to the expected carrier leakage signal, the sideband power can also be much stronger than the carrier leakage signal within the uncalibrated transmission branch. The first gain and phase imbalance is then compensated for at the maximum transmit power, followed by the LO leakage at reduced transmit power. For better results at maximum transmit power, gain and phase calibration are repeated.

9 (a) to 9 (c) show the receiver calibration, which is performed after the transmitter calibration. In the case of an AC coupled receiver, only the gain error is calibrated in the receiver branch 2. In the case of a DC coupled receiver, in addition to the gain error calibration, the DC offset error may be calibrated. After calibration of the transmitter, the signal constellation for the transmitted signal is optimal. With this optimal signal constellation, processor 61 closes switch 80 to perform receiver calibration. 9 (a) shows the error voltage V _error = | peak-peak (V _{I_R} ) _-peak -peak (V _{I_Q} ) | V _{I_R} and V _{I_Q} are shown in FIG. 1. 9 (c) shows that V _error = average value V _IR . As shown in FIG. 9 (a), the DAC 72 sweeps the gain signal ΔG ₂ and sets the optimal gain to G _{2, opt} . Gain sweeping can start from high gain, low gain or nominal gain. As shown in FIGS. 9B and 9C, the DC offset may be set to V _{3, opt} and V _{4, opt} by the DACs 69 and 70. In one scenario, V ₃ and V ₄ are set to some expected maximum DC offset below the maximum power reception, and then to the calibrated gain at the maximum power reception. To be more accurate, the calibration may be repeated at least once.

As described above, various modifications may be made within the spirit and scope of the invention as defined by the appended claims, and it will be apparent to those skilled in the art that the invention is not limited to the embodiments provided. The term "comprising" does not exclude the presence of elements or steps other than those described in a claim.

Claims (14)

A method of calibrating a transmit branch 3 of a transmitter, Measuring a low frequency component in the high frequency output signal V ₀ of the transmission branch 3, wherein the low frequency component is present when the transmission branch 3 is not calibrated; Derive a first compensation signal V ₁ from the measured low frequency components and inject the first compensation signal V ₁ into an in-phase branch of the transmission branch; 22, the second compensation signal (V ₂₎ to derive the second compensation signal (V ₂₎ to (23) for implantation in a quadrature branch (a quadrature branch) of the transmission branch; and Sweeping the first and second compensation signals V ₁ , V ₂ and adapting the first and second derived compensation signals based on the low frequency component. Wow, Obtaining minimum values (V _{1, opt} , V _{2, opt} ) of the measured low frequency component from the sweeping step, Setting the first and second compensation signals to the minimum values V _{1, opt} , V _{2, opt} Transmission branch calibration method comprising a. The method of claim 1, A transmission branch calibration method that repeats the sweeping step at least once. The method of claim 1, Injecting the compensation signals after each transmit filter (20, 21) step in the in-phase and quadrature transmission branches, wherein the set first and second compensation signals are local oscillator in the transmitter. Transmission branch calibration method to compensate for carrier leakage. The method of claim 3, wherein Sweeping gain and phase settings (ΔG ₁ , Δθ) within the transmission branch while measuring the low frequency component, Obtaining additional minimum values ΔG _{1, opt} , Δθ _{, opt} of the low frequency component during the sweep of the gain and phase setting; Setting the gain and phase settings to corresponding values of the additional minimum values ΔG _{1, opt} , Δθ _{, opt} , respectively. Transmission branch calibration method further comprising. The method of claim 4, wherein Set the gain and phase settings at a first transmit power of the transmitter, repeat the local oscillator carrier leakage compensation at a second transmit power of the transmitter, wherein the first transmit power is substantially different from the second transmit power. Transmission branch calibration method. The method of claim 5, And a transmission branch calibration method that repeats the gain and phase compensation at the first transmit power. The method of claim 1, Further comprising calibrating the receiving branch of the receiver 2, The transmitter 3 and the receiver 2 form a transceiver, The calibration step of the receiving branch Sweeping the gain setting in the receive branch during the measurement of an error signal (V _error ), Obtaining a smaller value of the error signal during the sweeping step of the gain in the receive branch; Setting the gain in the receive branch to a value ΔG _{2, opt} corresponding to the smaller value Transmission branch calibration method comprising a. As the transmitter 3, Send branch, Means for measuring a low frequency component in the high frequency output signal V ₀ of the transmission branch, the low frequency component being present when the transmission branch is not calibrated; Means 22 for inducing a first compensation signal V ₁ from the measured low frequency component and injecting the first compensation signal V ₁ into an in-phase branch of the transmission branch; and a second compensation signal V _2. Means for injecting the second compensation signal (V ₂ ) into the orthogonal branch of the transmission branch; Means for sweeping the first and second compensation signals (V ₁ , V ₂ ) and modifying the first and second induced compensation signals based on the low frequency component; Means for obtaining minimum values (V _{1, opt} , V _{2, opt} ) of the measured low frequency component from the sweeping, Means for setting the first and second compensation signals to the minimum values V _{1, opt} , V _{2, opt} Transmitter comprising a. The method of claim 8, Respective transmission filters 20, 21 in the in-phase and quadrature transmission branches, Means (22, 23) for injecting said compensation signal behind said respective transmission filter (20, 21), The set first and second compensation signals (V _{1, opt} , V _{2, opt} ) compensate for local oscillator carrier leakage in the transmitter (3). The method of claim 9, Means for sweeping gain and phase settings in the transmission branch while measuring the low frequency component; Means for obtaining smaller values of the low frequency component during the sweep of the gain and phase setting; Means for respectively setting the gain and phase settings to values corresponding to the smaller values ΔG _{1, opt} , Δθ _{, opt} The transmitter further comprises a. The method of claim 10, The transmitter is configured to set the gain and phase settings at a first transmit power of the transmitter, and to repeat the local oscillator carrier leakage compensation at a second transmit power of the transmitter, the first transmit power being the second transmit power. Transmitter 3 substantially different from power. As the transmitter 3, Send branch, Controller 60, An output signal detector 40 for measuring a low frequency component in said high frequency output signal V ₀ of said transmission branch, said low frequency component being present when said transmission branch is not calibrated, The controller derives a first compensation signal V ₁ from the measured low frequency component to inject the first compensation signal V ₁ into an in-phase branch of the transmission branch and injects a second compensation signal V ₂ . Induces to inject (23) the second compensation signal (V ₂ ) into an orthogonal branch of the transmission branch, The controller 60 sweeps the first and second compensation signals V ₁ , V ₂ , modifies the first and second induced compensation signals based on the low frequency component, and measures the measured from the sweep. Means for obtaining minimum values of a low frequency component and setting the first and second compensation signals to the minimum values V _{1, opt} , V _{2, opt} Transmitter comprising a. As the transceiver 1, A transmission branch 3, Means for measuring a low frequency component in the high frequency output signal V ₀ of the transmission branch, the low frequency component being present when the transmission branch is not calibrated; Means for inducing a first compensation signal (V ₁ ) from the measured low frequency component to inject the first compensation signal (V ₁ ) into an in-phase branch of the transmission branch, and inducing a second compensation signal (V ₂ ) Means for injecting (23) said second compensation signal (V ₂ ) into an orthogonal branch of said transmission branch, Means for sweeping the first and second compensation signals (V ₁ , V ₂ ) and modifying the first and second induced compensation signals based on the low frequency component; Means for obtaining minimum values of the measured low frequency component from the sweep; Means for setting the first and second compensation signals to the minimum values V _{1, opt} , V _{2, opt} Transceiver (1) comprising a. The method of claim 13, Further comprising a receive branch 2 for calibrating the receive branch, The transceiver includes means for sweeping a gain setting within the receive branch while measuring an error signal (V _error ); Means for obtaining a smaller value of an error signal during the sweep of the gain in the receive branch; Means for setting the gain in the receive branch to a value ΔG _{2, opt} corresponding to the smaller value Transceiver (1) comprising a.