2002, Issue 6, Category: Electronic Products and Devices
As we all know, in the wireless remote control transmitting and receiving circuit system, there are many radio frequency receiving circuits composed of discrete components, and the circuit board wiring is more complicated. Moreover, the frequency is high, the influence of the distributed parameters is also greater, and the circuit debugging is difficult. The radio frequency receiving integrated circuit can overcome the above shortcomings. The following uses the gy2800 integrated circuit as an example to introduce its composition, characteristics, principles and applications.
1. The composition and working principle of gy2800 integrated circuit The integrated circuit GY2800 is AM (Amplitude Modulation) return to zero amplitude shift keying RZ-ASK (Retum-to-Zero, Amplitude-schef-Keying) remote control receiving integrated circuit, which can be used for single-channel remote control receiving integrated circuit and transmitting data. Data communication or control. Compared with the receiving circuit composed of discrete components, it has fewer external components, is easy to debug, and can reduce the size of the circuit board, with lower cost and low power consumption. This integrated circuit can form a multi-channel remote control or signal transmission circuit system with commonly used codec integrated circuits, such as ED5026, ED5027 / 5028 and so on. Because the GY2800 output signal can also interface with the TTL level, it can be used as a data interface circuit of the microprocessor, and it is easy to form various wireless remote control systems.
The functional block diagram of gy2800 structure is shown in Figure 1. It is mainly composed of a two-stage pre-low-noise amplifier, a first-stage (third-stage) high-gain amplifier, a detection circuit, and a comparator. The third-stage amplifier consists of a single-ended to differential amplifier conversion circuit and a six-stage high-gain logarithmic amplifier composition.
2. Working principle: After the antenna receives the AM-RZ-ASK signal, it passes through the external band-pass LC matching network, enters the first-stage low-noise high-gain amplifier for amplification, and then passes through the pre-selection frequency filter to the second-stage high-gain amplifier. It is amplified and then amplified by the third-stage frequency selective amplifier. After detection, it is sent to the comparator circuit to generate a baseband pulse signal compatible with TTL level, and then output through a low-pass filter. At the same time, the output signal of the comparator is sent to the Manchester decoding logic circuit to output a trigger signal and a serial data signal. These output signals are meaningful only when the transmit encoding circuit uses Manchester encoded data. The trigger pulse indicates the start of each data bit received. This pulse can be used as the synchronous trigger pulse of the serial data decoder and the trigger pulse of the microcontroller to read the data. Similarly, the trigger signal output terminal and the serial data output Termination has a low-pass filter to suppress high-frequency interference.
2. Characteristics and technical parameters of gy2800 Main characteristics of gy2800:
1. The carrier frequency range is 200 ~ 450MHz (VHF / UHF band).
2. The receiving sensitivity is 20dB / μV.
3. The baseband data transmission rate is 500 Hz to 20 kHz.
4. Easy to interface with serial data encoding circuits and microcontrollers.
5. The internal sampling clock rate can be adjusted by external components.
6. Built-in logarithmic amplifier and comparator, smooth detection, adaptive offset threshold circuit, improve the circuit's receiving sensitivity and noise suppression performance.
7. There are few external components, soIC package.
8. Advanced BiCMOS technology, low power consumption.
See the attached table for technical parameters.
3. Typical application This integrated circuit can be used for single-channel remote control and data transmission system. The 10-channel remote control circuit system is introduced below.
1. Transmitting circuit Figure 2 shows the transmitting circuit. The encoding integrated circuit adopts VD5026 chip and 0 ~ 4 wire encoding integrated circuit 74LS147. It consists of triodes 3DG9018, C2, C3, C4, L1 and R1, R3. Controllable oscillator, L1 also doubles as transmitting antenna. The AM-RZ-ASK signal represents the data "1" with a continuous oscillation wave, and the data "0" does not oscillate, so the controllable oscillator is controlled by the VD5026 serial data code. Changing the value of C2 can fine-tune the transmission oscillation frequency to It is the same as the receiving frequency of the receiver. The transmitting frequency of this circuit is about 320MHz.
2. Receiving circuit Figure 3 is the receiving circuit. RF receiving uses gy2800 integrated circuit chip. The RF signal is received through the antenna and fed into the {18} pin of gy2800. After internal amplification, detection, and shaping, the serial data code is directly output from the BBOUT terminal and passes through the decoding circuit After the VDD5027 is decoded, it is then decoded by the 4 ~ 10 line decoder 74LS42, which can output 10 control signals corresponding to the transmitting circuit.
3. Installation and commissioning are shown in Figure 3. According to the values ​​of the components in the figure, the receiving frequency is about 320MHz. The receiving frequency mainly depends on the parameters of the external frequency selection network between the {20} and {24} pins and the {22} and {3} pins. These two frequency selection networks Optional surface acoustic wave filter or LC filter. Therefore, adjusting the values ​​of L1, C2, C7 and L5, C12 can change the receiving frequency of the receiving circuit. The quiescent current of the circuit shown in Figure 3 is about 30mA. Transmission frequency adjustment: The transmission circuit power supply adopts 6V power supply (or battery), and the transmission current is 6 ~ 10mA. First, use an oscilloscope to observe the serial code signal on the {17} pin of VD5026 in Figure 2. If there is a controllable oscillator that can oscillate, the transmitter circuit is 3m away from the receiver circuit, adjust the C2 trimmer capacitor, and align with the gy2800 reception frequency point. Use an oscilloscope to observe the pulse signal at the {14} pin of the GY2800 BBOUT terminal, and then fine-tune C2 to make the pulse waveform output amplitude larger. After this pulse signal passes through VD5027 and 4-10 decoder 74LS42, it can output the corresponding 10-channel control signal.
This monolithic RF receiving integrated circuit with coding and decoding integrated circuit can be widely used in data communication, home security system, telemetry data transmission, automatic door control system, vehicle anti-theft system. Compared with the receiving circuit composed of general discrete components, the integrated circuit chip has reliable performance, convenient application, simple debugging, few peripheral components and low power consumption, and is suitable for mass production. Therefore, it has broad application prospects.
? Guangdong Wang Yangzhao
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