An AC-coupled voltage follower is an operational amplifier circuit configuration that combines the properties of both an AC coupling network and a voltage follower (unity gain buffer). Here is a detailed explanation:
**Definition:**
An AC-coupled voltage follower is a unity-gain buffer amplifier with AC coupling capacitors at the input and output terminals to block DC components while allowing AC signals to pass through.
**Key Characteristics:**
1. **Voltage Gain**: The voltage gain of an AC-coupled voltage follower is unity (Av = 1) for AC signals. This means the output AC signal equals the input AC signal in magnitude and phase.
2. **Input Impedance**: The input impedance is very high (ideally infinite for an ideal op-amp), making it suitable for high impedance sources.
3. **Output Impedance**: The output impedance is very low (ideally zero for an ideal op-amp), enabling it to drive low impedance loads effectively.
4. **Frequency Response**: Due to AC coupling capacitors, the circuit has high-pass filter characteristics. The lower cutoff frequency is determined by the coupling capacitor value and the input/output impedance.
**Circuit Configuration:**
- The non-inverting input of the op-amp is connected to the input signal through a coupling capacitor (Cin)
- The output is connected directly to the inverting input (100% feedback)
- The output is coupled to the load through another capacitor (Cout)
- Both coupling capacitors block DC voltage while passing AC signals
**Applications:**
1. Signal buffering in AC-coupled amplifier stages
2. Impedance matching between high and low impedance circuits
3. Audio signal processing
4. AC signal transmission with DC blocking
5. Protection of circuits from DC offset voltages
**Advantages:**
- Very high input impedance
- Very low output impedance
- Unity gain for AC signals
- Good for driving loads without loading effects
- DC blocking prevents circuit saturation
**Disadvantages:**
- DC signals are blocked
- Frequency response limited by coupling capacitors
- Additional component cost
- Phase shift at lower frequencies
This configuration is commonly used in audio amplifiers, signal conditioning circuits, and AC signal processing applications where DC blocking and impedance matching are required.