Previous article "Direct RF Match Network Circuit Circuit Based on CMT2300A" We talked about several aspects when designing RF matches: port impedance matching must be consistent, insertion loss is as small as possible, with external decline is as possible Large, PA power and efficiency are as high as possible, and the components are as small as possible. Designed for CMT2300A RF matches, there are two matching methods of Direct Tie and Switch Type.
The previous story mainly said that the direct-connected radio frequency matching network circuit design is mainly written in the design of Refroject matching network circuit.
The Switch Type matches requires that the RF Switch is switched between the antennas to TX and RX channels. Compared with Direct Tie matching, the transmission and reception circuit is high, and it is easy to implement.
CMT2300A RF switch (switch type) matching circuit schematic design
1. L1 is a choke inductor.
2. C10-C14 is a power supply decoupling capacitor for reducing the impact of the PA output on the power supply.
3. C1 is a vertical capacitor, and part inductance to L2 is formed to harmonically inhibit the harmonic suppression.
4. C8 and C9 are coupled capacitors.
5. L2, C2 and C5 make PA output impedance and RF switch J2 foot impedance matching.
6. C6, L6, C7, L7 and L8 form a barrace matching network, implement the input impedance of the receiver and the RF switch J3 foot impedance match, and cause the received signal to reach the differential input port RFIP, the RFIN is equal, the amplitude is equal, the phase difference is different. 180 degree.
7. L3, C3, L4, C4 and L5 are low-pass filter networks, realize antenna and RF switch J1 foot impedance matching, suppress harmonics.
8. Y1 Recommended frequency tolerance ± 20 ppm 26MHz crystals, acceptable crystal frequency tolerance depends on the requirements of the user's product communication system, such as frequency, channel, bandwidth, and the like.
9. R1, R2 is a current limiting resistor.
10. C15, C16 is a crystal load capacitor (note the internal load capacitance of the chip has been integrated, 26 MHz crystals of CL = 15 pf, and the conversion crystal interconnect distribution capacitance 2PF, C4 and C5 are about 15 * 2 -4-2 = 24pf).
11. C17, C18 Filter capacitance, filter out the discharge signal on the antenna switch.
12. C19-C22 filter capacitor, the serial CSB, FCSB, SDIO, SCLK pin is easily interference, the larger the power output (20dBm), the lower the operating frequency, and interfering The larger the probability, it is recommended to reserve the area capacitor (27PF) near the four pins to filter out RF interference.
The CMT2300A RF switch matches PCB Layout as two-layer wiring design.
described as follows:
1. The radio frequency signal path is as low as short, and the loss of the radio frequency signal input and the output is reduced.
2. RF traces should be as flat as possible to reduce impedance fluctuations on the transmission line to produce reflection. In the above figure, the L2 to the P1 amplifier is 50 Ω impedance transmission lines. In this reference design, the double panel is FR4 sheet, the dielectric constant ER = 4.6, the copper thickness is 1 Iz, the PCB plate thickness is 0.8mm, and the width of the transmission line is about 1 mm, and the gap of the transmission line and the gap is set to When 0.35mm, the impedance of 50 ohms can be obtained.
3. Try not to have silk in the radio frequency path, the wire print will affect the transmission line impedance.
4. L1 is close to the PA pin. Adjacent inductors are placed in an orthogonal placement, which can reduce mutual coupling.
5. The radio frequency passage, the crystal circuit, and the neighboring layer of the crystal circuit and the IC have a complete laying (GND).
Our other product:
