Forehead
Wireless Frequency Identification (RFID) is an automatic ID technology that recognizes any object containing the encoding volume. The UHFRFID system consists of a reader (or interrogator) that changes the RF signal in the range of 860MHz to 960 MHz and transmits information to the volume label. In general, the volume label is passive, and it receives all the energy required for the reader of the sending continuous wave (CW) RF signal. The volume label responds through the reflection coefficient of the antenna, thereby reversing the information signal into the reader.
The volume signal detection requires the time interval between signal jaws (the time interval representing the data "1" symbol is longer than the symbol of the "0" representing the data. The reader transmits an indication of the volume to set its reverse scatter data rate and the number of signals to initiate the process of providing inventory information.
The RFID reader works in a plurality of readers to work closely adjacent to the RF environment. Single interrogator, multi-interrogator, and intensive interrogator These three working modes determine the spectrum limit of the reader and the volume label signal. The software programmable of the receiver makes it a balance between reliable multi-volume detection and high data throughput.
Programmable reader contains a high linear direct conversion I and Q demodulators, several low noise amplifiers, a variable gain and bandwidth dual channel baseband filter, and a dual channel analog digital converter (ADC ). Dual channel, matching, and programmable bandpass filter LTC6602 can optimize efficient RFID readers.
Dual channel bandpass filter
The LTC6602 has two identical filter channels, which have matching gain control and low pass and Qualcomm networks controlled by frequency. The phase shift per channel is matched to ± 1 degrees. The internal or external frequency frequency positions the passband of the filter to the desired spectrum.
The low pass and high-pass corner frequencies and the filter bandwidth are set by the scale ratio of frequency frequencies. The low-pass scale ratio option is 100, 300 and 600, and the high pass scale ratio is 1000, 2000, and 6000. Figure 1 shows a typical filter response, the filter appliance 90MHz internal frequency, high pass and low-pass scale ratios are set to 6000 and 600.4 order elliptical cut-off strip response help to eliminate out-of-band noise. Control the fundamental frequency bandwidth can define its operating mode with software during the RFID receiver to accommodate the working environment.
Figure 2 shows a simple and LTC6602-based filter circuit that uses SPI serial control to change the gain and bandwidth of the filter to accommodate a complex data rate and encoding. (The frequency range of the reverse scattering link is 40 kHz to 640 kHz, and the data rate range is 5 kbps to 640kbps.)
In order to achieve the fine resolution positioning of the filter, the internal frequency frequency is set by an 8-bit LTC2630 DAC. The DAC output range of 0V to 3V determines the position between 40 MHz to 100 MHz (234.4 kHz per bit). Low pass and high pass scales are set by the serial SPI control of the LTC6602.
The high pass filter has a cutoff of 6.7kHz to 100 kHz, while the low-pass filter is 66.7 kHz to 1 MHz. Filter bandwidth settings can be adjusted through a software algorithm, and is a function of data frequency, data rate, and encoded. The filter bandwidth must be narrow enough to expand the dynamic range of the ADC input, and it must be wide enough to protect the signal jump and pulse width (the correct filter setting ensures reliable DSP volume logo detection).
Figure 3 shows an example, that is, the filter pair a typical volume symbol sequence (a "short" pulse interval, followed by a time domain response of a "long" pulse interval). The low-pass cutoff frequency is set to be equal to the reciprocal of the short interval (FcutOff = 1 / 10μs = 100 kHz). If the low-pass cutoff frequency is lower, the signal jump and time interval will not be identified. The setting of the high-pass cutoff frequency is more qualitative instead of specific.
The high-pass cutoff frequency must be lower than the reciprocal of long intervals (in the example, high pass fcutoff < 1 / 20μs), and as high as possible to reduce the low frequency noise of the receiver (base frequency amplifier, and downconversion Phase and amplitude)). The lower half of Figure 3 displays the overall response of the filter (low-pass plus high pass filter).
The filter output of 10kHz and 30kHz high-pass settings, the signal jump and time interval for 10kHz output are sufficient for detection symbol sequences (in the RFID environment, noise will overlap on the output signal). In general, increasing low-pass Fcutoff and / or reduces high-pass Fcutoff means that the "quality" "quality" of the "improve" signal jump and time interval is increased to increase the output noise of the filter.
in conclusion
The LTC6602 dual-channel bandpass filter is a programmable fundamental frequency filter for efficient UHF RFID readers. Using the LTC6602 under software control can work with high data rate when the single service is physically set, or when the multi-interrogator or intensive interrogator is generated, the volume signal detection can be implemented. The LTC6602 is a very fine IC that is encapsulated by 4mm x 4mm QFN, and can be programmed by parallel or serial control.
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Source: Wiku Electronic Market Network
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