The design of analog circuit is the most headache engineers, but also the most deadly design part! We should pay attention to the problems in analog circuit design are summarized, share them with you.

(1) in order to obtain good stability of the feedback circuit, usually require on the outside of the feedback loop USES a little resistance or choke coil to provide a buffer capacitive load.

(2) the integral feedback circuit usually need a small resistance (about 560) and each is more than 10 pf the integration capacitor in series.

(3) do not use outside the feedback loop active filtering circuit or control EMC of RF bandwidth, and can only be used for passive components (best) for RC circuit. Only in the open loop gain of the op-amp is bigger than a closed-loop gain of frequency, the integral feedback method is valid. Under the higher frequency, the integral circuit can't control frequency response.

(4) in order to obtain a stable linear circuit, all connections must be suppressed using passive filter or other methods (such as photoelectric isolation), for their own protection.

(5) the use of EMC filter and the filter should be associated with IC and local reference plane 0 v connection.

(6) should be placed in the joint of outside cable input and output filter, all without the wire connection of the shielding system need to filter, because of the antenna effect. In addition, in the digital signal processing or switch mode of the wire connection of the shielding of the converter system also needs to filter.

(7) in the power of analog IC and need high quality reference pin and RF decoupling, this like the digital IC. But analog IC usually requires low frequency power supply decoupling, because analog components of power supply noise rejection ratio (PSRR) a little after higher than 1 KHZ. In each of the op-amp, comparator, and simulation of power converter go online should use RC or LC filter. Power filter corner frequency should compensate PSRR corner frequency and slope on the device, so as to work in the whole frequency range to obtain the desired PSRR.

(8) for high-speed analog signal, according to the length of the connection and communication of the highest frequency, transmission technology is necessary. Even the low frequency signal, the use of transmission technology can also improve its anti-interference, but there is no correct matching transmission line will produce a antenna effect.

(9) to avoid using high impedance input or output, it is very sensitive to the electric field.

(10) as most of the radiation is generated by common-mode voltage and current, and because most environmental electromagnetic interference are common mode, therefore in the analog circuits using the sending and receiving balance (differential mode) technology will have very good EMC effect, but also reduce crosstalk. Balance circuit (differential circuit) drive will not use 0 v reference system as the return current loop, so you can avoid large current loop, thus reducing the RF radiation.

Comparator (11) must have a lag (positive feedback), in order to prevent errors because of the noise and interference of output transformation, oscillation can also prevent the breaking point. Don't use more quickly than need comparator (dV/dt remain within the scope of the meet the requirements, as low as possible).

(12) some analog IC itself particularly sensitive to rf fields, so often need to use a installed on the PCB, and connected to the PCB ground plane of the small metal shielding box, simulation of such components for shielding. Note that to ensure the heat dissipation.