Transmitter with frequency measurement stage

Abstract

A transmitter (1) is configured to transmit a modulated transmitter data signal (2) in an aerial RF field and is configured to receive a modulated receiver data signal (8), the transmitter (1) comprising a transmitter stage (3) configured to generate the modulated transmitter data signal (2) with a certain frequency and waveform based on a carrier signal (5), an antenna (7) connected to the transmitter stage (3) via a matching circuit (12) of the transmitter (1) and configured to transmit the modulated transmitter data signal (2) in the aerial RF field, a receiver stage (9) connected to the antenna (7) via the matching circuit (12) and configured to receive the modulated receiver data signal (8), wherein the transmitter (1) comprises a measurement stage (13) to measure an actual resonance frequency (fpeak) of the antenna (7) and its matching circuit (12) connected to the transmitter stage (3) and the receiver stage (9).

Description

Technical Field

[0001] The present invention relates to a transmitter configured to transmit a modulated transmitter data signal in an RF field in the air and to receive a modulated receiver data signal. The transmitter includes: a transmitter stage configured to generate a modulated transmitter data signal having a specific frequency and waveform based on a carrier signal; an antenna connected to the transmitter stage via a matching circuit of the transmitter and configured to transmit the modulated transmitter data signal in an RF field in the air; and a receiver stage connected to the antenna via the matching circuit and configured to receive the modulated receiver data signal. Background Technology

[0002] Known Radio Frequency Identification (RFID) communication systems use integrated circuits such as the ST25R3916 in RFID readers or transmitters to communicate with active or passive receivers. In typical applications, a passive receiver (e.g., a transponder or tag) stores a product identifier of the product to which it is attached, and a transmitter (e.g., a reader) is used to obtain that product information. The transmitter is powered on and generates a magnetic RF field emitted by its antenna. When the transmitter and tag are close to each other, the RF field generated by the transmitter is induced in the tag's antenna and used to power the passive tag. The tag also has a transceiver for receiving signals from the reader and transmitting the response as a load-modulated receiver data signal back to the transmitter.

[0003] Standards such as ISO / IEC 18000-3, ISO / IEC 14.443 Type A and B, ISO 15.693, ECMA-340 13.56MHz Near Field Communication (NFC) or the NFC Forum, or company standards such as Sony's Felica, exist that define the protocols and modulation types used to transmit information between tags and readers. Some or all of these standards define the transmission of amplitude-modulated data signals containing digital data to tags using amplitude modulation within an RF field in the air. For example, ISO 14.443 Type A further defines the use of modified Miller coding to encode the data signal into an encoded data signal for transmission.

[0004] All these standards define the system frequency of the carrier signal to be used, such as 13.56 MHz for the NFC standard. Other RFID standards define carrier signals in the kHz or GHz frequency range. The antenna system of an active transmitter is tuned or regulated to resonate at the system frequency for maximum transmission range. Passive transponders are tuned or regulated to resonate at the system frequency to generate as much energy as possible from the RF field produced by the transmitter for internal power generation. The Nordic Semiconductor white paper, titled "nRF52832 NFC Antenna Tuning," discloses external test equipment such as oscilloscopes and signal generators for measuring the actual resonant frequency of a transmitter or passive transponder and tuning it to the system frequency. NXP Semiconductors' document "AN11535" discloses another complex and expensive test setup for measuring the actual resonant frequency.

[0005] Due to component tolerances, each individual transmitter may require different tuning of the variable capacitor in the matching circuit to ensure that the transmitter's actual resonant frequency is the system-defined resonant frequency. This is done at the end of the manufacturing process using such testing equipment. In some cases, components of the matching circuit are replaced because variable components are often more expensive and require manual adjustment. This tuning process may need to be repeated after the transmitter is installed in a specific application location, as the transmitter housing or other metal objects nearby in the RF field can affect the transmitter's actual resonant frequency. These tuning processes increase the technical complexity of the transmitter's manufacturing and implementation. Another disadvantage is that if the actual resonant frequency changes during the transmitter's use, for example, if a metal object is installed nearby in the transmitter's RF field, this can reduce the transmission range and potentially lead to system failure if communication between the transmitter and receiver does not operate within the system-defined communication range boundaries.

[0006] Prior art documents US2014 / 080409A1, EP1770665A1, US2018 / 034510A1 and JP2009111483A disclose a transmitter configured to transmit a modulated transmitter data signal in an RF field in the air and to receive a modulated receiver data signal. Summary of the Invention

[0007] The purpose of this invention is to reduce technical complexity and ensure that the transmitter conforms to the resonant frequency of a desired or system-defined RF field. This purpose is achieved by a transmitter that also includes a measurement stage for measuring the actual resonant frequency of the antenna and matching circuitry connected to the transmitter stage and the receiver stage.

[0008] This concept of measuring the transmitter's resonant frequency within the transmitter itself offers key advantages. Since there are no external test devices (which themselves affect the RF field and thus the measurement results), the transmitter's resonant frequency measurement is highly accurate. Furthermore, the resonant frequency can be measured at any time, such as each time the transmitter is powered on or during a period of its use. This allows for easy adaptation to events that affect the RF field and ensures compliance with standards throughout the transmitter's lifespan. In principle, the measurement results can be displayed on the transmitter to notify the operator that manual adjustment of the resonant frequency is required. In a preferred embodiment, the transmitter includes control logic that activates an adjustment mode after the actual resonant frequency measurement has been completed and adjusts the actual resonant frequency to the desired or system- or standard-defined resonant frequency via a tuning variable capacitor. This variable capacitor can be part of an external matching circuit or part of the transmitter's integrated circuit. The control logic implemented in the transmitter's integrated circuit manipulates the external or internal variable capacitor.

[0009] This technique has never been used or implemented in integrated circuits that generate and transmit carrier signals, where the resonant frequency of the carrier signal must be measured and adjusted. The claimed transmitter with a measurement stage uses a carrier signal stage that scans frequencies within a relevant frequency range and measures the actual resonant frequency of the antenna system, which consists of the antenna, the transmitter's matching circuitry and integrated circuits, and some other metallic devices in the vicinity of the RF field. To measure the actual resonant frequency, an unmodulated sine wave of the transmitter data signal is used to avoid interference caused by a carrier frequency that is several times higher than other waveforms (such as square waves). This is analyzed by mixing the received unmodulated receiver data signal with the actual carrier signal, and a DC compensation stage retrieves the DC signal portion at 0 Hz of the mixer's output signal. These DC signal portions of different actual carrier signals within the frequency range are used to generate a frequency peak signal to illustrate the DC signal portion within the frequency range. The frequency with the maximum amplitude of this frequency peak signal is the measured actual resonant frequency of the transmitter's antenna system. Based on the measured actual resonant frequency, a variable capacitor tuned antenna system can be used to move the actual resonant frequency to the system-defined resonant frequency during manual or automatic adjustment. In another embodiment of the invention, the received unmodulated receiver data signal is analyzed by mixing it with the actual carrier signal and adding an offset frequency as the mixer signal, and the signal portion of the mixer's output signal at this offset frequency is used to generate the frequency peak signal.

[0010] These and other aspects of the invention will be apparent from and set forth with reference to the embodiments described below. Those skilled in the art will understand that various embodiments can be combined. Attached Figure Description

[0011] Figure 1 A first embodiment of a transmitter according to the invention is shown, which is used to transmit amplitude-modulated data signals and measure the actual resonant frequency of the transmitter's antenna system.

[0012] Figure 2 The frequency peak signal is shown, which has the error between the measured actual resonant frequency of the transmitter's antenna system and the system-defined resonant frequency.

[0013] Figure 3 A second embodiment of the transmitter according to the invention is shown, which is used to transmit amplitude-modulated data signals and measure the actual resonant frequency of the transmitter's antenna system. Detailed Implementation

[0014] Figure 1A transmitter 1 according to a first embodiment of the present invention is shown. The transmitter 1 is used to transmit an amplitude-modulated transmitter data signal 2 to a receiver of an RFID communication system in an RF field in the air. The transmitter 1 includes a transmitter stage 3 having a wave generator 4 for generating the amplitude-modulated transmitter data signal 2 with a specific frequency and waveform based on a carrier signal 5. A clock generator 10 provides an internal clock signal 23, and the wave generator 4 is capable of generating a sine wave wave by wave at the frequency of the carrier signal 5, as known from the applicant's EP3182585B1. The wave generator 4 also includes an amplifier for amplifying the generated amplitude-modulated transmitter data signal 2. The prior art document discloses a digital power amplifier that generates a sine wave by small increments of M digital waveform forming bits, which accumulates the increments of the output current to generate the sine wave. For this purpose, the wave generator 4 receives the clock signal 23 from the clock generator 10 at a frequency that is a multiple (e.g., 64 times) of the frequency of the carrier signal 5 to generate a sine wave with the frequency of the carrier signal 5. The RFID communication system conforms to the NFC standard ISO 18.092, which defines a resonant frequency of 13.56 MHz for the carrier signal 5 with a sinusoidal waveform. The RFID communication system also conforms to ISO / IEC 14.443 Type A and B, or ISO 15.693, or ECMA-340 13.56 MHz. Transmitter 1 is implemented in integrated circuit 6 and provides amplitude-modulated transmitter data signal 2 via amplifiers at antenna pins Ant_p and Ant_n on integrated circuit 6. In this embodiment, antenna pins Ant_p and Ant_n are connected to transmitter stage 3 via two lines and to receiver stage 9 via two lines; the amplitude-modulated transmitter data signal 2 and the modulated receiver data signal 8 are differential signals. Matching circuit 12 is connected to antenna pins Ant_p and Ant_n and impedance-matches the antenna 7. Matching circuit 12 and antenna 7 are arranged to resonately transmit the amplified amplitude-modulated transmitter data signal 2 to a nearby receiver, which can be implemented as a passive or active tag or any other active device, such as a mobile phone. Even when there is no receiver in the RF field of transmitter 1, interference from things in the RF field and the effects of matching circuit 12 and antenna 7 result in unmodulated or modulated receiver data signals 8 received, particularly at antenna pins Ant_p and Ant_n.

[0015] Transmitter 1 includes a receiver stage 9 connected to antenna 7 via antenna pins Ant_p and Ant_n and via matching circuitry 12, for receiving modulated receiver data signal 8. Receiver stage 9 includes a mixer 11 for mixing the received modulated receiver data signal 8 with a carrier signal 5 generated by carrier signal stage 24 based on clock signal 23 from clock generator 10. Clock signal 23 and carrier signal 5 are always in a fixed relationship because the frequency of clock signal 23 is a multiple of carrier signal 5. Transmitter 1 also includes a waveform measurement stage for measuring the shape of the received modulated receiver data signal 8 using equivalent time sampling. Equivalent time sampling is known to those skilled in the art and enables the capture of periodic signals at an effective sampling rate much higher than the actual sampling rate of the AD converter used. During each repetition of the periodic signal, other portions of the waveform are sampled and combined in post-processing of the sampled data to provide a high-resolution signal. The use of such equivalent time sampling in oscilloscopes is known to improve the detail of the measured and displayed signal. The transmitter 1, which has its waveform measurement stage, performs waveform measurement based on equivalent time sampling of the received modulated receiver data signal received in the RF field generated by the transmitter 1 itself. This technique is described in another patent application filed on the same day and is unrelated to the invention claimed in this patent application.

[0016] The transmitter 1 according to the present invention includes a measurement stage 13 and a matching circuit 12. The measurement stage 13 is used to measure the actual resonant frequency fpeak of the antenna system affected by the antenna 7. The matching circuit 12 is connected to the transmitter stage 3 and the receiver stage 9. peak It may also be affected by metallic devices in the RF field or other effects known to those skilled in the art. Measurement stage 13 includes control logic 14 for activating the measurement mode of transmitter 1 and manipulating clock generator 10 to scan the frequency of clock signal 23. This causes wave generator 4 to generate a clock signal 23 with a frequency that is a multiple of the frequency of carrier signal 5, having a resonant frequency f at a desired or system-defined resonant frequency f. target The transmitter data signal 2 is a frequency within the centered frequency range. In this embodiment of the invention, the wave generator 4 is configured to generate the transmitter data signal 2 having a carrier signal 5 with a system-defined NFC resonant frequency f of 13.56 MHz. target .like Figure 2As shown, in this embodiment, the frequency range of the frequency scan in the measurement mode is fixed, ranging from 13.2MHz to 15MHz. Due to this frequency scan of the clock signal 23 provided to the carrier signal stage 24 in the measurement mode, the frequency of the carrier signal 5 provided to the mixer 11 changes from 13.2MHz to 15MHz during one frequency scan. One or more frequency scans can be performed during the measurement mode. The frequency range mentioned above is just an example, and it can cover a wider or narrower range in this frequency region or another frequency region.

[0017] Transmitter 1 includes mixer 11, which provides an output signal A, such as Figure 1 As shown in Figure 18, the output signal A includes an amplitude of 2 × 13.56 MHz (=27.12 MHz) and a DC component of 0 Hz. This DC component is relevant to further processing because it contains information about the actual amplitude of the receiver data signal 8 at a specific actual frequency during the frequency scan manipulated by control logic 14, such as... Figure 2 As shown.

[0018] Receiver 9 also includes a DC compensation stage 15 connected to mixer 11 to retrieve the DC signal portion of the output signal A of mixer 11 as the amplitude of the received modulated receiver data signal 8 at a specific actual frequency manipulated by control logic 14. Referring to the applicant's patent EP3267589B1, which describes the main function and use of the DC compensation stage 15 (= the DC elimination stage in EP3267589 B1), the DC compensation stage 15 is a feedback loop for eliminating the DC component at a 0Hz frequency for further signal processing of the received modulated data signal 8 from another NFC device in the RF field. For the present invention disclosed herein, the DC component determined by the DC compensation stage 15 is used for the measurement. Receiver 9 also includes an AD converter stage 16 for sampling the amplitude of the analog output signal A of mixer 11 as digital data to be stored in control logic 14 for a specific actual frequency of frequency scanning. At the end of the measurement cycle, measurement stage 13 generates, based on the digital data stored in control logic 14, a signal such that... Figure 2 The frequency peak signal 17 shown is used to accumulate all the digital data of the output signal A at different frequencies during frequency scanning. Figure 2 The system-defined resonant frequency f is also shown. target and the measured actual resonant frequency f peak How must be Figure 2 The change in frequency difference is shown as the error.

[0019] Transmitter 1 includes a variable capacitor 19, which is implemented within the integrated circuit 6 of transmitter 1 to measure the actual resonant frequency f. peak Adjust to the system-defined resonant frequency f target Control logic 14 is configured to activate the adjustment mode and manipulate the variable capacitor 19 to deliver the measured actual resonant frequency f. peak Adjust to the system-defined resonant frequency f target This makes the error zero in the adjustment mode. Those skilled in the art of integrated circuit design know how to implement the variable capacitor 19 within integrated circuit 6, and how to adjust its variable capacitor using signals or manipulation commands from control logic 14. In another embodiment of the invention, the capacitor 19 implemented within integrated circuit 6 can be manipulated by an external manipulation signal to adjust the measured actual resonant frequency f. peak Adjust to the system-defined resonant frequency f target In another embodiment of the invention, the variable capacitor may be implemented externally to the integrated circuit 6 as part of the matching circuit 12. In this embodiment, the control logic 14 adjusts the variable capacitor using signals or manipulation commands on the pins of the integrated circuit 6.

[0020] In another preferred embodiment of the invention, control logic 14 is configured to switch between a measurement mode and an adjustment mode to adjust the actual resonant frequency f during the iteration process. peak Adjust to the system-defined resonant frequency f target This allows for very precise tuning of the resonant frequency.

[0021] The transmitter 1 with measurement stage 13 of the present invention can be used during testing of new transmitter settings (e.g., matching) to optimize the reader design using the transmitter's integrated circuits. For these tests, the receiver may or may not be arranged within the reader's RF field. However, the transmitter 1 with measurement stage 13 of the present invention can also be used during normal use of the reader to retune the resonant frequency of the reader's RF field.

[0022] In another embodiment of the invention, the variable capacitor is implemented within the transmitter's integrated circuit, and another variable capacitor is implemented outside the transmitter's integrated circuit in the matching circuit. This allows for tuning of the resonant frequency over a wide range.

[0023] In another embodiment of the invention, a variable inductor can also be used to adjust the measured actual resonant frequency to the resonant frequency defined by the system or standard.

[0024] exist Figure 3In another embodiment shown, clock generator 10 provides its clock signal 23 to mixer signal generator 25, which is configured to provide mixer 11 with a frequency different from or similar to that of carrier signal 5. Figure 1 In this embodiment, the mixer signal 21, with a frequency that is a multiple of the carrier signal 5 (clock signal 23), is used for frequency scanning. As an example, the mixer signal 21 during frequency scanning can be a frequency multiple of the carrier signal 5 (clock signal 23). Figure 1 In the embodiment, the carrier signal stage 24 provides a frequency 200 Hz higher. This means that the wave generator 4 produces an unmodulated transmitter data signal 2 with a sinusoidal waveform and an actual frequency varying from 13.2 to 15 MHz during a single frequency scan, while the mixer signal 21 is always, for example, 200 Hz higher than the generated actual frequency. This results in... Figure 3 Chart 22 in the chart does not contain anything like... Figure 1 The DC component is like that in f, but in f mix The frequency component at 200Hz contains information about the actual amplitude of the receiver data signal 8 at a specific actual frequency during the frequency scan manipulated by control logic 14. To evaluate the amplitude of this frequency component, control logic 14 is configured to control the AD converter stage 16 to oversample the mixed-down signal of mixer 11 and calculate the amplitude of the output signal A shown in Figure 22. As a result of this calculation, a frequency peak signal 17 is again generated at the end of the measurement mode. This embodiment shows that the actual frequency signal used for transmission and the mixed signal 21 used to mix the received data signal 8 do not necessarily have the same frequency or a multiple of the same frequency. However... Figure 1 The embodiment shown has the advantage that it does not require control logic 14 to calculate the relevant components as described above.

[0025] In another embodiment, the mechanism can keep the frequency of the mixer signal 21 constant and scan only the frequency of the unmodulated transmitter data signal 2 in the measurement mode.

[0026] In addition, Figure 3 In the embodiment shown, the antenna pin Ant_n is connected to a defined potential, and the antenna pin Ant_p is connected to the transmitter stage 3 via a line and to the receiver stage 9 via a line, and the amplitude-modulated transmitter data signal 2 and the modulated receiver data signal 8 are signals related to the defined potential.

[0027] Furthermore, based on Figure 1 In another embodiment of the invention, carrier signal stage 24 can provide carrier signal 5 to a modulator that replaces wave generator 4. The data signal to be transmitted can be fed to this modulator, which modulates the data signal using carrier signal 5. Other functions are as follows: Figure 1 As described in the embodiments.

Claims

1. A transmitter (1) configured to transmit a modulated transmitter data signal (2) in an RF field in the air and configured to receive a modulated receiver data signal (8), the transmitter (1) comprising: The transmitter stage (3) is configured to generate the modulated transmitter data signal (2) with frequency and waveform based on the carrier signal (5). The antenna (7) is connected to the transmitter stage (3) via the matching circuit (12) of the transmitter (1) and is configured to transmit the modulated transmitter data signal (2) in the RF field in the air. The receiver stage (9) is connected to the antenna (7) via the matching circuit (12) and is configured to receive the modulated receiver data signal (8). The transmitter (1) includes a measurement stage (13) configured to measure the actual resonant frequency (f) of the antenna (7). peak ); and its matching circuit (12), the matching circuit (12) being connected to the transmitter stage (3) and the receiver stage (9), wherein the measurement stage (13) includes control logic (14), the control logic (14) being configured to activate the measurement mode and being configured to manipulate the clock generator (10) of the transmitter (1) to achieve a desired or system-defined resonant frequency (f) in the measurement mode. target The transmitter stage (3) scans the frequency of the carrier signal (5) and / or the mixer signal (21) within a frequency range centered on the transmitter (5), wherein the transmitter stage (3) includes a wave generator (4) configured to generate an unmodulated transmitter data signal (2), and wherein the control logic (14) is configured to manipulate the wave generator (4) to transmit the unmodulated transmitter data signal (2) having a sinusoidal waveform and a frequency scan of the carrier signal (5) in the measurement mode, wherein the receiver stage (9) includes a mixer (11) configured to receive the unmodulated transmitter data signal (2 ...) having a frequency scan of the carrier signal (5) and / or the mixer signal (21) in the measurement mode, wherein the receiver stage (9) includes a mixer (11) configured to receive the unmodulated transmitter data signal (2) and / The receiver data signal (8) is mixed with the carrier signal (5) of the carrier signal stage (24) of the transmitter (1), characterized in that the receiver stage (9) includes a DC compensation stage (15) connected to the mixer (11) and configured to extract the DC signal portion of the output signal (A) of the mixer (11) as the amplitude of the received unmodulated receiver data signal (8) at the frequency (f) of the carrier signal (5) manipulated by the control logic (14), and is configured to generate a frequency peak signal (17) at the end of the measurement mode.

2. The transmitter (1) according to claim 1, wherein the transmitter (1) includes a variable capacitor (19) configured to transmit the measured actual resonant frequency (f) peak Adjust to the system's defined resonant frequency (f) target ).

3. The transmitter (1) according to claim 2, wherein the transmitter (1) is implemented as an integrated circuit (6), wherein only the antenna (7) and the matching circuit (12) are outside the integrated circuit (6), and the matching circuit (12) is connected to the antenna pin (Ant_p; Ant_n) of the integrated circuit (6), and the variable capacitor (19) is part of the matching circuit (12) outside the integrated circuit (6) or the variable capacitor (19) is part of the integrated circuit (6).

4. The transmitter (1) according to claim 3, wherein the control logic (13) is configured to activate an adjustment mode and is configured to manipulate the variable capacitor (19) to adjust the measured actual resonant frequency (f) in the adjustment mode. peak Adjust to the system's defined resonant frequency (f) target ).

5. The transmitter (1) according to claim 4, wherein the control logic (13) is configured to switch between a measurement mode and an adjustment mode to measure the actual resonant frequency (f) during the iteration process. peak Adjust to the system's defined resonant frequency (f) target ).

6. The transmitter (1) according to any one of claims 1 to 5, wherein the carrier signal stage (24) is configured to generate the system-defined NFC resonant frequency (f) having a frequency of 13.56 MHz. target The carrier signal (5) of the carrier signal.

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