Sensitivity Test Methods and Characteristics of Active Filter Amplifiers

Active filtering amplification circuits are often used in electronic systems with high frequency stability requirements to improve the stability and power level of crystal oscillator signals. However, active filtering amplifiers may also receive electromagnetic interference signals from the other systems in the same environment. Even if it is an out of band electromagnetic interference signal, it may cause abnormal output of the active filtering amplifier, leading to malfunction. Therefore, this paper designs a sensitivity test method for out of band electromagnetic interference excitation filter amplifier circuits based on the basic working principle of filter amplifier circuits, and studies the sensitivity law of active filter amplifiers. In this proposed method, a directional coupling based port conduction sensitivity testing method is proposed, and three kinds of interference signals (sine signal, pulse modulation signal, and frequency offset modulation signal) are considered for excitation. The relationships between the frequency and amplitude of the excitation signal and the output signal of the active filter amplifier are studied. The experimental results show that the proposed method can be used for effectively evaluted the sensitivity phenomenon of the active filtering amplifier. At the same time, it can be seen that the signal-to-noise ratio emission of the output signal of the active filter amplification circuit significantly decreases (exceeding 10 decibels) under the effects of out of band sine, pulse modulation, and frequency offset modulation; and exhibits a typical "threshold initiation" characteristic.