Application of MDO Mixed Domain Oscilloscope in IoT Design, R&D and Training
chrispeng [ad_1]
The development trend and design challenges of the Internet of Things industry
With the development of modern sensor technology and wireless communication technology, the Internet of Things has begun to enter people’s daily lives. IoT applications represented by technologies such as RFID, ZigBee technology and NFC near-field communication are becoming the direction of R&D and innovation for many enterprises and universities. Although semiconductor manufacturers provide various dedicated chips and even highly integrated solutions for these technologies, engineers still face many challenges when designing an actual IoT device. One of the most important factors is how to measure the time-dependent time-domain and frequency-domain signals in the system. Although the RF signal applied in RFID and ZigBee technology is not very complicated, the quality, power and timing relationship of the signal determine whether the system can work normally. These RF parameters are not only related to the radio frequency transmitting/receiving circuit, but also affected by the baseband circuit and the control circuit. The reading and writing of internal registers, the working condition of the power supply and even the size of the system delay time will determine the working status of the entire system. Traditional oscilloscopes or spectrum analyzers cannot complete this time-related comprehensive debugging of time-domain and frequency-domain signals.
Innovative design concept of MDO mixed domain oscilloscope
The unique innovative concept of the Tektronix MDO4000 series mixed domain oscilloscope provides a unique tool for debugging cross-domain time-frequency related systems. On the basis of a full-featured mixed signal oscilloscope, MDO4000 adds a 3GHz or 6GHz spectrum analyzer, which can complete various frequency domain measurement functions of ordinary spectrum analyzers. Completely independent oscilloscope time domain acquisition system and spectrum analyzer frequency domain acquisition system, which can work independently or work together through triggers. By moving the spectrum time, the user can observe the spectrum of the RF signal at any point collected on the RF channel within the time window collected by the oscilloscope. MDO also provides the modulation domain analysis function of the amplitude, frequency, and phase of the RF signal with respect to time. These unique functions help users measure various modulation information of RF signals. A problem that engineers who use spectrum analyzers often face is how to accurately trigger and capture the RF signal of interest. Due to the limited trigger function of traditional spectrum analyzers, it is difficult for users to do that. MDO4000 can not only trigger through various characteristics of RF signal, but also use the trigger system of oscilloscope to complete the trigger acquisition of RF signal through baseband or control signal. This function greatly reduces the difficulty of modulating IoT devices.
When debugging an RFID system, an important difficulty faced by engineers is how to measure the return signal of the tag. Since the amplitude of the signal returned by the tag is very small, it is often difficult to capture this signal with an ordinary oscilloscope, let alone further analysis of its amplitude and frequency. The main reason is that the dynamic range of an ordinary oscilloscope is only 40dB, which cannot capture weak tag signals. MDO4000 has a dynamic range of 60dB and a noise floor as low as -152dB/Hz, which is well-suited for the task of simultaneously capturing reader signals and tag signals. Its unique AvsT radio frequency signal amplitude time-domain waveform function can even display the change process of the tag signal amplitude.
Below we take a 13.56MHz RFID reader system as an example to introduce the cross-domain debugging application of MDO4000.
Application of MDO Mixed Domain Oscilloscope in the Research and Development of RIFD System
Figure 1 RFID reader with NXPCLRC632 chip
Test the RF signal quality parameters of 13.56MHz RFID reader
The 13.56MHz high frequency RFID system is currently the most widely used radio frequency identification system in China with relatively mature technology. Relevant international standards have clear requirements for parameters such as radio frequency transmission frequency, channel bandwidth, transmission power, etc. In particular, the standard has strict regulations regarding the changes in the amplitude (power) of the RF signal over time. Take the reading and writing device as an example, the amplitude change time of the carrier signal sent by the reading and writing device must comply with the time limit of t1-t4 in the ISO18000-3 standard.
Figure 2 ISO18000-3 13.56MHz RFID air interface time parameter specification
By using the unique trigger function of MDO4000, users can easily and stably capture the time domain and frequency domain signals of RFID. As shown in the figure, because the amplitude of the carrier signal is changing, it is difficult to measure the time length of the RF signal from 90% to 5% of T1 using traditional methods. We can open the AvsT modulation curve, which represents the trajectory of the amplitude of the RF signal with respect to time. Through automatic measurement or manual cursor measurement, we can easily get the accurate time of T1. In the same way, other time parameters can be tested.
Figure 3 Time domain and AvsT modulation domain waveforms from 13.56MHz RFID PCD to PICC signal
Figure 4 Measuring the delay time between the PCD transmit signal and the tag return signal
Test the read and write time from PCD to PICC
Another time that needs to be strictly guaranteed is the time from when the reader sends the card reading signal to when the tag returns the signal. Too long or too short a time will be regarded as read and write failure. It is very difficult to measure these signals with traditional instruments. MDO4000 can completely display the AvsT trace of the RF signal on the screen. Users only need to locate the corresponding position with the cursor to get this delay time.
Figure 5 Time domain waveform, modulation domain waveform and spectrum display of 13.56MHz RFID radio frequency signal
The RFID system that uses the ASK modulation method transmits data information through subcarriers. In the frequency spectrum part of the above figure, we can clearly see that the carrier of the radio frequency signal is 13.56MHz, and the subcarrier signal is about ±800KHz. Meet the requirements of relevant regulations. If you need to measure the RF parameters of the RF signal, such as channel power, adjacent channel power ratio or occupied bandwidth, you can directly display these measurement results on the screen by selecting the automatic measurement function of MDO4000.
[ad_2]
