Bandpass Amplifier and Rejection Amplifier

Bandpass Amplifier:

1. Frequency Response:
• A bandpass amplifier is designed to amplify signals within a specific frequency range, known as its passband.
• Within Passband: The magnitude (gain) of the amplifier is at its maximum within this range. The amplifier effectively amplifies signals whose frequencies fall within the passband.
• Outside Passband: Outside this range, particularly at frequencies lower than the lower cutoff frequency and higher than the upper cutoff frequency, the magnitude significantly decreases. This is due to the roll-off characteristic of the amplifier, which attenuates frequencies outside the passband.

2. Magnitude Plot:
• The Bode magnitude plot of a bandpass amplifier shows a peak or plateau within the passband frequencies and a roll-off at frequencies below and above this range.

Rejection Amplifier (Notch Filter or Band-Stop Filter):

1. Frequency Response:
• A rejection amplifier, or notch filter, is designed to attenuate or reject signals within a specific frequency band, allowing other frequencies to pass with minimal attenuation.
• At Rejection Band: The magnitude significantly decreases at the specific frequencies it's designed to reject, creating a "notch" in the frequency response.
• Outside Rejection Band: At frequencies outside this rejection band, the filter has little effect on the signal, and the magnitude remains relatively high or only slightly affected.

2. Magnitude Plot:
• The Bode magnitude plot for a notch filter shows a significant dip at the rejection frequencies and a relatively flat response at other frequencies.

Key Differences:

• Bandpass Amplifier: Amplifies a specific range of frequencies (passband) and attenuates frequencies outside this range—the magnitude plot peaks within the passband.

• Rejection Amplifier (Notch Filter): Attenuates a specific range of frequencies (notch) and allows other frequencies to pass with minimal attenuation. The magnitude plot dips at the notch frequencies.