Programmable Filter

What is a Programmable Filter?
Programmable filter devices for arithmetic and various other processing.
The test was carried out by using a digital synthesis signal source, a dual-trace oscilloscope, a simulator, and an AC voltmeter. Adjust the frequency of the input signal, and use the AC voltmeter to record the effective value of the output voltage, and compare and analyze the actual measured value and the preset value.

Programmable filter system is proposed in the deficiency of traditional filter. Traditional filters produce errors during operation, which will affect the accuracy of the entire system. Low-precision filters will cause many adverse consequences when used, and the higher the waveform requirements of traditional filters, the more operational amplifiers are needed, which is very troublesome. Therefore, the digitalization of the program-controlled filter can reduce the uncertain factors and the number of human-involved links in the production process, and can effectively solve engineering problems such as reliability, intelligence, and product consistency in the power module. Greatly improve production efficiency and product maintainability.

Programmable filter introduction
The signal picked up by the measurement system from the sensor often contains noise and many signals that are not related to the measured, and the original measurement signal is transmitted, amplified, transformed, calculated, and various other processing processes. Various forms of noise can also be mixed in, affecting measurement accuracy. These noises are generally highly random and difficult to separate directly from the time domain, but limited to the mechanism of their generation, their noise power is limited, and they are distributed in a specific frequency band in the frequency domain according to certain rules. The signal separation circuit generally uses a filter to suppress noise and extract the required measurement signal. However, the form and cut-off frequency of the filter used in the system are often fixed, and it is difficult to be adjustable, which brings some inconvenience to the system design. However, the use of switched capacitor filters can solve this problem very well, but the price of switched capacitor filters is relatively high, which will increase the design cost of the system.

The core part of the programmable filter
The core part of the system is the biquad loop filter, which uses more than two operational amplifier circuits composed of adders, integrators, etc., and introduces appropriate feedback components according to the required transfer function. filter circuit. Its outstanding feature is that the circuit has low sensitivity, so its characteristics are stable, and it can realize various filtering functions. Appropriate improvements can also reduce the number of operational amplifiers. This system adopts TI's four-channel operational amplifier OPA404, and designs a double second-order loop filter circuit. OPA404 is a four-way high-speed precision operational amplifier with a voltage slew rate of up to 35 V/s, which can meet the design requirements of this system.