Typically, when designing a RF matches, there is a need to take care of: the impedance matching of ports must be consistent, the insertion loss is as small as possible, and the extraception is as large as possible, the 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.
Direct Tie matching circuit without RF switches, TX and RX path impedance transformations directly to the antenna. CMOSTEK DIRECT TIE matches the circuit structure, with fewer components, which can meet the CE / FCC specification, and achieve high receiving sensitivity, high efficiency, and high-power output.
1. L1 is a choke inductor.
2. C8-C11 is a power supply decoupling capacitor for reducing the impact of the PA output on the power supply. Adjust appropriately according to the actual application needs.
3. C1 is a vertical capacitor, and part inductance to L2 is formed to harmonically inhibit the harmonic suppression.
4. The A point identified above is a direct connection, which is 50 Ω.
5. L2, C2 and L3 constitute a TX matching network, implement the PA output and direct connection impedance matching.
6. C6, L6, C7, L7, L8 form the RX bar playback network, realize the input impedance of the receiver and the direct connection matching, and cause the received signal to reach the differential input port RFIP, the RFIN is equal, the phase phase difference is 180 degrees. .
7. L4, C3, L5 is a T-type low-pass filter matching network of 50Ω to 50Ω.
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. C4, C5 is a crystal load capacitor (note that the internal load capacitance of the chip has been integrated, 26 MHz crystals of CL = 15 pf, and the distribution capacitance of the alcoholic contact-connected wire distribution capacitance 2PF, C4 and C5 is about 15 * 2 -4-2 = 24pf).
10. C12-C15 filter capacitor, the serial CSB, FCSB, SDIO, SCLK pin is easily interfected in the line unreasonable or trails, the larger the power output (20dBm), the lower the operating frequency, and interfered The larger the probability, it is recommended to reserve the area capacitor (27PF) near the four pins to filter out RF interference.
Recommended Customer Reference CMOSTEK Direct (Direct Tie), the network between TX and RX paths to direct connecting points is used to use the officially recommended part of the same value. The antenna matching filter network (L4, C3, L5), to adjust the step and component value of the filter to the CE / FCC specification according to the antenna impedance, cost requirements. If the board area is limited, it is recommended that L1-L8 still uses high Q value laminate 0603 inductance (such as SunLORD SDCL1608 series), but the capacitance can be encapsulated by a 0402 package.
CMOSTEK Direct Tie 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. The lines of the L2 to P1 are 50 Ω impedance transmission lines in the above figure. 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 branch network of direct connection points (above the C2, L7, and C7 elements of the above) should be short.
6. The radio frequency passage, the crystal circuit, and the neighboring layer of the crystal circuit and IC have a complete laying (GND).
7. TX and RX passways must have GND networks to isolate.
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