RC Filters Flashcards
An RC filter is a circuit constructed from ____ and ____ that will block certain frequencies and pass others.
An RC filter is a circuit constructed from capacitors and resistors that will block certain frequencies and pass others.
Remember, as frequency (increases or decreases), capacitive reactance (increases or decreases).
Remember, as frequency increases, capacitive reactance decreases.
What does an RC filter circuit block or pass?
Frequency
What is the difference between these two RC filters configurations?
Left - Low pass filter passes low frequencies while blocking high frequencies.
Right - High pass filter passes high frequencies while blocking low frequencies.
An RC low pass filter consists of a capacitor and a resistor. The input is applied in series with ______. The output is taken from across the ______.
An RC low pass filter consists of a capacitor and a resistor. The input is applied in series with the resistor. The output is taken from across the capacitor.
The basic operation of an RC low pass filter is that at low frequencies, C1 has a __________. Most of the input signal is developed across the capacitor and is passed to the output.
The basic operation of an RC low pass filter is that at low frequencies, C1 has a large capacitive reactance. Most of the input signal is developed across the capacitor and is passed to the output.
The basic operation of an RC low pass filter is that at high frequencies, C1 has a ________. Most of the input signal is shunted to ground by the low reactance and not passed to the output.
The basic operation of an RC low pass filter is that at high frequencies, C1 has a small capacitive reactance. Most of the input signal is shunted to ground by the low reactance and not passed to the output.
In a low pass filter circuit, where is the capacitor placed, in relation to the output signal?
In parallel
Remember, low pass filters pass low frequencies. The capacitor is placed in parallel with the output so, at low frequencies, a large capacitive reactance (Xc) develops most of the output signal.
Depicted in the graph, the low frequencies are passed and the high frequencies are blocked. Where is the changeover from passed to blocked?
The changeover occurs when the output power of the circuit is half the maximum value or the half power point. This point is an electronic industry standard and is equal to the frequency called cutoff or fco. This produces 0.707 (70.7%) of the maximum voltage.
In the example circuit, the half power point is where the voltage output is 0.707 of 12 Vpp or about 8.5 Vpp. An output voltage of 8.5 occurs at approximately 20 kHz. fco is about 20 kHz.
Frequencies below fco (low pass filter) pass through the circuit to the output. These are the ______.
Frequencies below fco pass through the circuit to the output. These are the pass band frequencies.
Frequencies above fco are attenuated, or blocked, from the output. These are the ________.
Frequencies above fco are attenuated, or blocked, from the output. These are the stop band frequencies.
What formula is used to find RCO?
FCO = 1 ÷ (2)(pie)(R)(C)
An RC high pass filter consists of a capacitor and a resistor, just like the low pass filter. What is the difference between the low and high pass filter?
The high pass input is applied in series with the capacitor.
The output is taken across the resistor. This is also important for identifying an RC high pass filter.
The basic principle of a RC high pass filter operation is that, at low frequencies, C1 has a ________.
The basic principle of a RC high pass filter operation is that, at low frequencies, C1 has a large capacitive reactance.
Most of the input signal is dropped across the capacitor and does not reach the output (the voltage across the resistor).
At high frequencies, C1 in this RC high pass filter has (High or Low) capacitive reactance.
At high frequencies, C1 in this RC high pass filter has low capacitive reactance.
The low Xc does not drop very much voltage, so most of the input signal reaches the output resistor.
