PCB manufacturing and PCB assembly factories
| The key to analo circuits is to learn more and do more. When making a film, you naturally know that you must master these knowledge points. Today, the editor summarizes twelve issues that should be paid attention to in the design of analo circuits for everyone. Let's take a look! |
| (1) In order to obtain a stable feedback circuit, it is usually necessary to use a small resistor or choke outside the feedback loop to provide buffering for capacitive loads. |
| (2) Since most of the radiation is generated by common-mode voltage and current, and because most of the environmental electromagnetic interference is generated by common-mode problems, balanced transmission and reception (differential mode) techniques are used in analo circuits It will have a good EMC effect and can reduce crosstalk. Balanced circuit (differential circuit) drivers do not use the OV reference system as a return current loop, thus avoiding large current loops and reducing RF emissions. |
| (3) Avoid using high-impedance inputs or outputs that are very sensitive to electric fields. |
| (4) The input and output filters should be placed at the connection of the external cables. Any wiring within an unshielded system will require filtering due to antenna effects. In addition, filtering is required at the wiring within the shielding system of a vehicle converter using digital signal processing or switch mode. |
| (5) EMC filters should be used, and all IC-related filters should be connected to the local 0V reference plane. As with digital ICs, the power and ground reference pins of analo ICs require high-quality RF decoupling. However, analo integrated circuits generally require low frequency power decoupling because the power supply noise rejection ratio (PSRR) of analo components barely increases above 1kHz. RC or LC filtering is applied to the analo supply lines of each op amp, comparator, and data converter. The corner frequency of the power filter should compensate the PSRR corner frequency and skew of the device so that the desired PSRR is obtained over the entire operating frequency range. |
| (6) In order to obtain a stable linear circuit, all connections must be protected by passive filters or other suppression methods such as opto-isolation. |
| (7) EMC filters should be used, and all IC-related filters should be connected to the local OV reference plane. |
| (8) For high-speed analo signals, transmission line technology is necessary according to the connection length and the highest frequency of communication. Even for low-frequency signals, the use of transmission line techniques can improve their immunity to interference, but without properly matched transmission lines, antenna effects can occur. |
| (9) Outside the feedback loop, do not use active circuits to filter or control the RF bandwidth of EMC, but only use passive components (preferably RC circuits). The integral feedback method is only effective when the open-loop gain of the op amp is greater than the closed-loop gain. At higher frequencies, the integrating circuit cannot control the frequency response. |
| (10) The integral feedback circuit usually requires a small resistor (about 560Q2) in series, and each integral capacitor is greater than 10PF. |
| (11) Some analo ICs are particularly sensitive to radio frequency fields, so it is often necessary to shield such analo components with a small metal shielding box mounted on the PCB and connected to the PCB ground plane. Take care to make sure the cooling straps are in place. |
| (12) The comparator must have hysteresis (positive feedback) to prevent erroneous output transitions due to noise and interference and oscillations at breakpoints. Use the comparator no faster than required (to keep DV/dt within acceptable limits and as low as possible). |
| analo electronics cover almost the entire electronic field. The functional realization of any electronic circuit involves analo circuits. The design of analo circuits is usually more difficult than digital circuits, and the level of designers is also higher. This is one of the reasons why analo circuitry is more popular than digital circuitry. |
