Application circuit of surface acoustic wave resonator in radio remote control

In order to welcome the advent of the information age and satisfy the readers' thirst for information and wireless transmission application technologies, this newspaper cooperated with Shenzhen Chuangsuojia Electronics Co., Ltd. to jointly develop the "application of surface acoustic wave devices in high-frequency wireless transceiver circuits". Application" column. In the column, based on Sokia's successful experience gained from continuous exploration in the field of high-frequency wireless transceivers over the years, combined with the latest modern software/hardware technology, it is divided into 5 chapters to introduce the use of surface acoustic wave devices in high-frequency wireless transceiver circuits. and the application of high-frequency wireless transceiver components in the field of information transmission. The content of the article is novel and practical, especially in the application of technology. It is believed that the launch of this column will provide useful help to professional technicians and people in the industry who are engaged in the development of radio application technology. Before we launched the SAW frequency-stabilized transmitter, most domestic manufacturers used a transmitter circuit published in overseas publications (for details, see page 53 of the first issue of "Practical Electronics Digest" in 1993 "Production with Surface Acoustic Wave Resonator" "Small Multi-Function Remote Control" article), the simplified circuit principle is shown in Figure 1. The designed output power of this circuit is 4mW. Compared with the LC transmitter with a designed power of 10mW, it is natural that the remote control distance becomes shorter. In fact, the oscillation circuit shown in Figure 1 is not the only form of surface acoustic oscillation circuit. After years of exploration, the author has designed and developed a variety of SAW frequency-stabilized oscillation transmitter circuits that can meet different needs, from microwatt-level micropower transmitters to single-stage high-power transmitters with output power of several watts, and From ASK (amplitude keying) or FSK (frequency shift keying) modulation mode digital transmission or remote control transmitters to AM (amplitude modulation) or FM (frequency modulation) mode voice and image transmission transmitters have been successfully developed. A high-performance radio remote control circuit with a maximum remote control distance of up to 3,000 meters on open ground is introduced to the majority of electronics enthusiasts. 1. Transmitter This is a four-button miniature ultra-remote remote control transmitter with address coding. The circuit principle is shown in Figure 2. R11~R13, Q1, and Q2 form an electronic switching modulation circuit. When the encoder output is high level, Q1 is turned on, and the oscillation transmitting stage works; when the encoder output is low level, Q1 is cut off, and the oscillating transmitting stage stops working, thereby completing ASK modulation. R14, Q3, C1, L1, L2 and surface acoustic resonator SAW form a 315MHz power oscillation stage. Q3 is a high-frequency power field effect transistor that can output 1.5W power at 450MHz, among which L1, L2 and C1 forms SAW The required phase shifting frequency selection and matching network enable Q3 and SAW to work at high efficiency. L3, C2 and C3 form an antenna matching network to match the antenna impedance with the oscillation stage to ensure its stable operation. The main technical specifications of the transmitter are as follows: 1) Working voltage range: 3V ~ 12V; 2) Working frequency: 315MHz ± 100kHz, other frequencies can also be selected; 3) Frequency stability: better than 10-5; 4) Peak transmit power: 0.5W; 5) Working temperature range: -20℃～+80℃; 6) Number of address codes: 6561 groups, non-repeating; 7) Working mode: intermittent work; 8) Overall dimensions: 73mm×37mm×15mm. The coding and button control parts of this machine are similar to those of general remote control transmitters. The featured parts are the modulation stage and the oscillation transmitting stage, which adopt my own original single-stage medium-power oscillation transmitting circuit. This is the reason for the miniaturization, low power consumption and long distance of this machine. Remote control guarantee. 2. Receiver The receiver is a superheterodyne finished board that uses a surface acoustic resonator to stabilize the frequency. The circuit principle is shown in Figure 3. The receiver uses the integrated circuit RX3310 as the core component to form an ASK demodulated super external MHz receiver with a sensitivity of -105dBm. The ① and ② pins of RX3310 are the connection terminals of the local oscillation circuit components. The local oscillator signal can be generated by connecting an external LC frequency selection network. In order to improve the stability of the unit, the local oscillator signal is generated by an external surface acoustic stabilizer oscillation circuit and is input through pin ①. The demodulated data signal is sent to the decoder for decoding from the ⑧ pin output. The main technical specifications of the receiver are as follows: 1) Working voltage range: 2.7V~5V; 2) Working frequency: 315MHz±100kHz, other frequencies can also be selected; 3) Working current: ≤3mA (when powered by 3V); 4) Receiving Sensitivity: better than -105dBm; 5) Working temperature range: -20℃～+80℃; 6) Address code/data: eight-bit three-state address/four-bit data; 7) Working mode: continuous working; 8) Overall dimensions: 28mm×32mm×5mm. 3. Application Since the transmitting and receiving parts of this set of components use surface acoustic wave resonators for frequency stabilization, they work stably and have long remote control distances, which can fully meet the stability and reliability requirements of industrial and civilian products. The design of this set of components fully takes into account the requirements of multi-purpose and scalability, and is widely used in remote remote control operations in security products, garage doors, traffic control, vehicle models, ship models, industrial automatic control and other fields. The remote control distance of this set of components on open ground is usually up to 1.2 to 1.5 kilometers. If it is powered by a 12V battery pack or DC stabilized power supply, the remote control distance can be up to 2 kilometers. If the antenna is replaced with a small suction cup Antenna or coaxial dipole antenna, the remote control distance can reach more than 3 kilometers. What needs special explanation is: the transmitter circuit is designed according to the requirements of intermittent operation, so the time of each button press shall not exceed 1 second, and the on/off ratio shall be less than 1. Mismatched antenna impedance will also affect the transmission effect and even damage the launch tube, so the rod antenna must be pulled out completely before launching. 