This design to be discussed herein can remove differential circuits in the bandpass filter scheme, and H. Martinezetal. The program attribute provided by the H. Martinezet is retained.
The bandpass filter (BPF) is widely used in a very narrow passband, any other frequency attenuated outside the passband.
Equation (1) is a second-order belt transmission function of a band pass filter:
Where k represents a constant filter gain, Q represents the quality factor of the filter.
In the article written in H.martinezetal, a bandpass filter with an adjustable quality of the tuning frequency point is described in the resonant frequency point with a band pass filter using three op amp designs. The transmission function of this filter meets the formula (1), where K is contrary to the quality factor Q. This bandpass filter with an adjustable quality factor consists of a dual T unit and a differential circuit.
This design to be discussed herein can remove differential circuits in the bandpass filter scheme, and H. Martinezetal. The program attribute provided by the H. Martinezet is retained.
In the band pass filter block diagram shown in Figure 1A, there is a voltage follower using IC1 and IC2, which can be implemented with a standard dual operation and connecting its inverted input to the op amp output.
Figure 1: This active belt pass filter scheme (a) can change the quality factor while maintaining the gain coefficient of the resonant frequency point. It is based on a double T unit (B) structure without a differential amplifier.
The band pass filter shown in Fig. 1 is based on a dual T-type structure (Fig. 1B).
The gain function formula of the filter designed according to (Equation 2 in Reference 1) is:
Where M is a positive feedback coefficient provided to the dual T unit (Fig. 1B) and is independent of frequency. The value of the quality factor depends on the position of the potentiometer RPOT. At the bottom position of the potentiometer, the quality factor Q of the cursor display filter is at the minimum, and when the potentiometer is adjusted upward, the quality factor increases.
The positive feedback coefficient m is defined as:
The resonant frequency of the active filter is:
The quality factor Q of Equation 2 is:
According to H.martinezetal. [1], the maximum gain amax is always unchanged when ω = ω0, and is equal to 1 (0 dB), and is independent of Q. M = 0 When the quality factor is minimized, the value is 1/4, and the rotor corresponding to the potentiometer is connected to the input. The biggest gain is theoretically infinite, but the quality factor in practical applications is difficult to reach 50 or more. The variation of Q in the typical application ranges from 1 to 10.
Figure 2 shows the bandmap when the band pass filter output VBP (S) / VIN (S) is changed from 0.1 to 0.9. As can be seen from the figure, the frequency f0 is equal to 1 kHz. The modeling of the filter is implemented using the "Spectrumsoft" (ECAD) Micro-CAP9 circuit emulation program.
Figure 2: The amplitude and phase portchart of the band pass filter output Vout (T). The figure shows the effects generated when the positive feedback coefficient M from the dual T-type unit from 0.1 to 0.9 is shown.
Our solution is achieved by moving the input voltage source Vin (T), the original scheme of the notch filter consisting of IC1 and IC2 is achieved.
Thus, the recommended circuit will be excluded from the additional differential circuit IC3 (Fig. 3B) to achieve similar results with Martinezetal (Fig. 3A).
Figure 3: Two options have the same transmission function.
(A) - Martinezetal.
(B) - Our design. , Reading the full text, the technology area
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