Electronics Engineering (ELEX) Board Practice Exam

What frequency range does a band pass active filter using an operational amplifier provide a constant output?

1. From f₀ to f_oh

2. From f₀₁ to f_oh

3. From 0 Hz to f_oh

4. From f₀ to f₁

The correct answer is: From f₀₁ to f_oh

A band pass active filter allows signals within a certain frequency range to pass while attenuating signals outside that range. The frequency range is determined by the design of the filter, specifically the selected components like resistors and capacitors in conjunction with the operational amplifier. The constant output is maintained between specific cutoff frequencies, known as the lower cutoff frequency (f₀) and the upper cutoff frequency (f_oh), establishing the bandwidth of the filter. Within this band, the filter will have a relatively stable gain, meaning it amplifies signals effectively without major variations. In this context, the correct choice specifies the range starting from the lower cutoff frequency (f₀) up to the upper cutoff frequency (f_oh). This clearly defines the operational effectiveness of the band pass filter, where signals can be reliably processed. Other ranges, like including frequencies below f₀ or completely different bands, would not yield the desired characteristics of a band pass filter. Such options do not capture the specific operational behavior of the filter as outlined by its fundamental design.