Microwave Tech - High-frequency board related production technology

High-frequency board related production technology

High-frequency board printed circuit design technology

(1) Transmission line width The design of the transmission line width of high-frequency circuit boards must be based on impedance matching theory.

When the output impedance matches the transmission line impedance, the output power of the system is the largest (the total power of the signal is the smallest), and the input reflection is the smallest.

The signal line passing through the hole will cause the change of the impedance transmission characteristic, and the characteristic impedance of the TTL and CMOS logic signal line is negligible.

However, the influence of low impedance and high-frequency circuit boards must be considered, and the value of 50 ohms must be considered, and signal lines should generally not pass through holes.

(2) Crosstalk between transmission lines

When the space between two parallel parallel microstrip lines is very small, a coupling produces crosstalk between the lines and affects the characteristic impedance of the transmission line. In particular, special attention should be paid to the high frequency circuits of 50 ohm and 75 ohm.

This coupling characteristic is also used in the actual design of circuits, such as power measurement and power control of mobile phones. The following analysis is valid for high-frequency circuits and high-speed (clock) data lines. Reference value for microwave circuits, such as precision operation amplifier circuits.

Assumption: The degree of coupling between the lines is equal to the degree of coupling of C, and the size of C and the length of the parallel straight line, such as R, W/D, S, L and L. The smaller, the stronger the connector; in order to improve the perception of knowledge An example is: a 50 ohm directional coupler.

In this feature,

For example, 1.97% PCS base station power amplifier, where D = 30 MHz, EPSIRON R = 3.48: Directional coupler circuit board size 10Db: S = 5mil, L = 920mil, W = 53MIL Directional coupler circuit board size 20db: S = 3mil, L = 920mil, W = 62MIL 2. In order to reduce the crosstalk between signal lines,

The following suggestions should be made:

a. The distance between parallel signal lines for high-frequency or high-speed data is greater than twice the line width.

b. Reduce the length of parallel signal lines.

C, small high-frequency signal, used to avoid the use of logic signal lines and logic signal low signal and other generous interference sources.

(3) Electromagnetic analysis from the ground launch hole. Solder the IC device or any other resistance to the ground, in the high frequency circuit, as close as possible to the brush head.

Because the land use line is very short, the transmission line on the earth is equivalent to the inductive impedance (n-pH magnetic), and the hole in the earth is approximately equivalent to the inductive impedance, which affects the filtering efficiency of high-frequency signals.

In the soil on the soil, the surface capacity of the low-frequency circuit is increased to ensure that all locations are zero.

Power filter In order to reduce the influence of signal logic on the power supply (overrun), TTL and CMOS circuits have added filter capacitors near the power socket, but it is not enough for high-frequency and microwave circuits to take such measures.

In the manufacturing process, the high-frequency signal is used as an example to illustrate the high-frequency signal. The high-frequency signals of these two methods produce high-frequency interference to the power supply and affect other functional circuits.

In addition to the power supply and filter capacitors, series inductors are also required to suppress high-frequency interference.

The inductance is selected, if the inductance is added to the open circuit signal column of the external power collector, because the inductance at this time is equivalent to the corresponding inductance.

Shielding When designing low-frequency and high-frequency signals, shielding measures should be taken to reduce high-frequency signal interference (such as logic level) or electromagnetic radiation.

a. When designing small digital and low-frequency signal (less than 30 MHz) printed circuits, apart from the separation of digital and analog, a reduced signal wiring area should be set, and the distance between the earth and the signal line should be greater than the width line.

b. When designing high-frequency and low-frequency digital and analog circuits, shielding or isolation should be added to the high-frequency part.

c. When designing high-frequency and high-signal circuits, independent functional modules and shielding boxes should be used to reduce the radiation of high-frequency signals.

Such as receiving and sending optical fiber 155M, 622M and 2GB/module. A multi-layer printed circuit board (NOKIA 6110), back reader, and portable phone circuit board design.

Examples of selection of printed circuit boards for high boards An example of the present invention is a high-frequency circuit (microwave) designed and developed by us to illustrate the center's choice.

(1) Choose the microwave relay relay card with 2.4 GHz spectrum. We use FR4 card, four printed circuit boards, a large paving panel, a high-frequency analog analog power supply using inductive blackout coils, and the digital part Isolation. The 24 GHz RF transceiver uses an F4 double panel, the transceiver and the transceiver are protected by a metal box, and the absorbed power is filtered.

(2) 1.9 GHz RF transceiver PTFE card is used for power amplifier, double-sided printed circuit board, PTFE card used for radio transceiver and four-layer printed circuit board, the circuit board adopts all high surface heat insulation measures and functional modules Protective cover.

(3) Fi-140 mhz transceiver The upper layer is composed of wide S1139 mm, pavement, and S1139 mm plates separated by holes.

(4) Transceiver 70 MHz We are using FR4 card and four-layer printed circuit board. Large area protection tape, functional module insulation tape and beam isolation series. Power amplifier 30W We used RO4350 board and a double-sided printed circuit board.

(5) Large-area bedding, the spacing or equal spacing on the 50 ohm line width, shielded by the metal box, and power input filter.

(6) 2000 mhz microwave frequency Use 0.8 mm thick S1139 card, double-sided printed circuit board.