A 10 kHz even-symmetric square wave is passed through a bandpass filte...
Answer:
Bandpass Filter:
A bandpass filter allows only a specified range of frequencies to pass through it while attenuating all other frequencies.
Given Parameters:
- Input signal: 10 kHz even-symmetric square wave
- Centre frequency of bandpass filter: 30 kHz
- 3 dB passband of bandpass filter: 6 kHz
Explanation:
1. Frequency Spectrum of the Input Signal:
- The Fourier series of an even-symmetric square wave contains only odd harmonics.
- The 10 kHz even-symmetric square wave has odd harmonics at 30 kHz, 50 kHz, 70 kHz, and so on.
- Therefore, the frequency spectrum of the input signal has a peak at 30 kHz and other odd harmonics.
2. Bandpass Filter Characteristics:
- The bandpass filter has a centre frequency of 30 kHz and a 3 dB passband of 6 kHz.
- This means that the filter allows frequencies in the range of 27 kHz to 33 kHz with maximum amplitude, and attenuates all other frequencies.
3. Output Signal:
- Since the input signal has a peak at 30 kHz, which lies in the passband of the filter, the filter allows this frequency to pass through it.
- The other odd harmonics of the input signal lie outside the passband of the filter and get attenuated.
- Therefore, the output signal is a nearly perfect cosine wave at 30 kHz.
Hence, option 'C' is the correct answer.