Switched-Capacitor DC Blocking Amplifier Without Off-Chip Capacitors
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Solution Overview
Problem
Integrated amplifiers for high-quality audio and video devices require high-pass filtering, which typically uses off-chip DC blocking capacitors, increasing the bill of materials, cost, and circuit board area, especially in multi-channel systems.
Innovation Solution
The implementation of on-chip switched capacitor circuits provides high resistance for biasing the amplifier input, eliminating the need for off-chip capacitors by using on-chip capacitors and switched capacitor circuits to create large resistance values, thereby reducing BOM, cost, and circuit area while addressing aliasing and distortion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If off-chip DC blocking capacitors are used for high-pass filtering, then DC components are removed from the input signal, but the bill of materials, cost, and circuit board area increase
Solution Approach 1:
The patent combines the DC blocking capacitor and amplifier into a single integrated circuit device. The capacitor is formed within the same semiconductor substrate as the amplifier, eliminating the need for separate off-chip capacitors. This integration maintains the high-pass filtering function while reducing external components, BOM, and board area.
Solution Approach 2:
The capacitor is nested within the amplifier circuit structure, sharing the same physical package and substrate. The capacitor plates are formed using the same semiconductor processing layers as the amplifier transistors, effectively hiding the capacitor within the amplifier's internal architecture rather than requiring external placement.
2Reliability
If off-chip DC blocking capacitors are used, then signal amplification quality is maintained, but the required circuit board area increases
Solution Approach 1:
By merging the capacitor and amplifier into one integrated device, the physical footprint on the circuit board is dramatically reduced. The entire high-pass filtering and amplification function is contained within a single component package, eliminating the space required for separate capacitor placement and associated trace routing.
3Quantity of substance
If switched capacitor circuits are used to provide high resistance for biasing, then off-chip capacitors are eliminated, but aliasing and distortion issues must be addressed
Solution Approach 1:
The patent employs feedback mechanisms within the amplifier circuit to compensate for aliasing and distortion introduced by the switched capacitor circuit. The feedback loop detects output errors and adjusts the input signal accordingly, maintaining signal fidelity despite the presence of switching artifacts.
Solution Approach 2:
The switched capacitor circuit uses periodic switching at a high frequency to simulate high resistance values that would be impractical to implement with physical resistors. By changing the switching frequency and capacitor values, the circuit achieves the desired biasing conditions while managing aliasing through proper frequency selection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces the need for external components, lowers costs, and minimizes circuit area while ensuring high-quality signal amplification and effective alias suppression, improving power supply noise rejection and distortion performance.
Implementation Method 1
a capacitive coupling to couple an input signal to an amplifier input of the amplifier
Implementation Method 2
The switched capacitor circuit is connected between the input and output of the amplifier and provides a large resistance to bias the amplifier
Data Source
AI summary
A switched-capacitor DC blocking amplifier is disclosed. In an embodiment, an integrated circuit is provided that includes an amplifier having an amplifier input and an amplifier output, a capacitor connected to the amplifier input and configured to receive an input signal, and a switched capacitor circuit coupled to provide a resistance between the amplifier input and the amplifier output. In one implementation, the switched capacitor circuit is configured with a feed forward circuit to reduce aliasing. In another implementation, the switched capacitor circuit includes a switched impedance circuit to reduce noise.