I. Power Filter Parameters
1. Center Frequency: The passband frequency f0 of the filter, typically taken as f0 = (f1 + f2) / 2, where f1 and f2 are the left and right sideband frequencies of the bandpass or bandstop filter, respectively, with a relative drop of 1dB or 3dB. Narrowband filters often use the point of minimum insertion loss as the center frequency to calculate the passband bandwidth.
2. Cutoff Frequency: This refers to the right-hand frequency of the passband of a low-pass filter and the left-hand frequency of the passband of a high-pass filter. It is typically defined by a 1dB or 3dB relative loss point. The reference for relative loss is: for low-pass filters, the insertion loss at DC is used as the reference; for high-pass filters, the insertion loss at a sufficiently high passband frequency without parasitic stopbands is used as the reference.
3. Passband bandwidth (BW x dB): This refers to the width of the spectrum that needs to be passed through. BW x dB = (f2 - f1). f1 and f2 are the left and right frequency points corresponding to a drop of X (dB) from the insertion loss at the center frequency f0. Typically, X = 3, 1, and 0.5, i.e., BW3 dB, BW1 dB, and BW0.5 dB, are used to characterize the filter's passband bandwidth. Fractional bandwidth = BW3 dB/f0 × 100 [%] is also commonly used to characterize the filter's passband bandwidth.
4. Insertion Loss: The attenuation of the original signal in the circuit due to the introduction of the filter. It is characterized by the loss at the center or cutoff frequency. If full-band insertion loss is required, it should be emphasized.
5. Ripple: refers to the peak-to-peak value of insertion loss fluctuating with frequency on the basis of the mean loss curve within a 1dB or 3dB bandwidth (cutoff frequency).
II. What are the effects of low temperature on filters?
(I) The impact of low temperature environment on the overall performance of filter
In addition to the performance changes of the aforementioned filter components, low-temperature environments may also affect the overall performance of the power supply filter through other mechanisms:
1. Component parameter variations: Low temperatures can cause changes in the parameters of components such as capacitors and resistors, directly affecting the filter's filtering characteristics and causing its performance to deviate from the design values. These changes may manifest as an increase in in-band insertion loss and a decrease in out-of-band rejection capability.
2. Filler Expansion: Some filter components use fillers to improve performance stability. However, at low temperatures, the fillers may expand, putting pressure on the internal structure of the component and thus affecting the filter's performance.
3. Temperature gradient: When the filter operates in a low-temperature environment, a temperature gradient will form inside it. Prolonged operation may cause thermal stress inside the components, affecting the reliability and lifespan of the components, and thus affecting the overall performance of the filter.
(II) Response Strategies
To mitigate the impact of low-temperature environments on the performance of power supply filters, the following strategies can be adopted:
1. Select high-quality components: Choose components such as capacitors and resistors with excellent temperature stability to ensure that the filter can maintain stable performance in low-temperature environments.
2. Use of special low-temperature materials: Special materials with excellent low-temperature performance are selected to manufacture filter components for use in low-temperature environments, thereby improving the filter's cold resistance.
3. Optimize filter design: By optimizing the filter design structure, such as adding heat dissipation devices and improving component layout, the internal temperature gradient can be reduced, thereby reducing component damage caused by thermal stress.
4. Strengthen testing and verification: During the filter design and manufacturing process, strengthen the testing and verification of performance under low temperature conditions to ensure that the filter can still meet the design requirements under low temperature conditions.
