How to make the recognition rate of the RFID reader reach 100%? Now, if we want to stably read the distance of 10 meters, let the recognition rate of the RFID reader reach 100%, and be able to adapt to changes in antenna feed and environment, read Is the effect better than ordinary products? The following Xiaobian from Shenzhen Xinye Intelligent Factory will answer your questions:

1. Analysis:

What are the influencing factors of receiver performance to be analyzed first?

UHF RFID reader receivers also require transmitters to transmit unmodulated carriers. DC offset is a disturbance specific to zero-IF structures, which is caused by LO coupling. Transmitter leakage and ambient reflected signals at the receiver to the mixer input. Therefore, since the reader transmits and receives at the same frequency, its DC offset is much larger than that of a conventional receiver. In addition, the common working distance is only 3-5 meters, and the carrier leakage is also affected by the antenna feed and the environment, so the DC offset is time-varying. The DC bias not only destroys the DC operating point of the post-stage circuit, but also affects the linear performance of the amplifier and filter, deteriorating the signal-to-noise ratio. With a single antenna design, the isolation degree of the circulator is limited to the transmission leakage and reception strength, and the DC offset problem will be more serious. In addition to improving the simulation of radio frequency circuits, corresponding measures must be taken in the algorithm of baseband signal processing.

2. Exercise:

Baseband Digital Signal Processing (1) Oversampling and filtering According to the Nyquist sampling theorem, in order to make the sampled signal return to the original continuous signal, the sampling frequency should be at least twice the highest frequency of the signal. Sampling can reduce the effective bandwidth of the quantization noise power and improve the signal-to-noise ratio, which is equivalent to improving the resolution of the ADC. For oversampled data, a CIC filter can be used to extract the data rate back to a normal level. Then, cascaded FIR filters are used for band-pass filtering to further reduce the noise power and improve the signal-to-noise ratio.

(2) DC migration correction

The methods of dealing with DC migration in circuit hardware include: exchange coupling, carrier cancellation, harmonic mixing, self-correction compensation, etc. Among them, the harmonic mixing processing and self-correction compensation methods are more complicated, and the implementation effect is limited, and there is a need to eliminate the carrier wave. The processing method, adding analog RF and baseband units and software methods in the compensation circuit, increases the complexity and cost, and makes debugging difficult. As mentioned earlier, a simple AC capacitive coupling method can filter out the DC portion of the signal to reduce the interference of DC offsets. This method is the simplest and cheapest of all solutions, and therefore the most widely used.

(3) Data decoding

Baseband data decoding methods are divided into zero-crossing detection and coherent detection. The working principle of zero-crossing detection is to set a threshold and compare the data buffer in each data sample with the median value. If the absolute value of the data and the sample is greater than If the difference between the thresholds is greater than the average value, it is determined to be 1, or it is determined to be 0. Because the method is simple and easy to implement, and even a comparator can be used to implement decision-making, it is widely used in low-end reader products.

The advantages of RFID technology are more reflected in group reading, and the core of this advantage lies in the anti-collision algorithm. When we buy, we can choose a good product, a good process design, and some necessary fault tolerance mechanisms, which will affect the read and write performance of RFID products. This also involves the realization of 100% recognition rate of RFID in the actual application process.