Flipped Voltage Follower Input Buffer With Frequency-Dependent Impedance
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Solution Overview
Problem
Existing input buffers face challenges in achieving high linearity and low output impedance, particularly in the low-frequency region, due to the suppression of loop gain by small resistors, which affects their ability to perform effective high-to-low resistance transformation.
Innovation Solution
A flipped voltage follower is configured in a pseudo-differential or single-ended architecture with a frequency-dependent impedance circuit, including capacitors and resistive elements, to maintain loop gain and reduce output impedance, ensuring high linearity and efficient resistance transformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If small resistors are used in the input buffer circuit, then the circuit can operate, but the loop gain is suppressed and output impedance cannot be sufficiently reduced
Solution Approach 1:
The patent changes the impedance characteristic from frequency-independent to frequency-dependent by introducing a capacitor in parallel with the resistor. This creates a frequency-dependent impedance circuit where the impedance varies with frequency, allowing the circuit to achieve low output impedance at signal frequencies while maintaining stability at DC and low frequencies.
Solution Approach 2:
The patent introduces dynamic behavior to the impedance circuit by adding a capacitor, making the impedance time-varying and frequency-dependent. This dynamic impedance circuit adapts its characteristics across different frequencies, providing low impedance at operating frequencies while maintaining proper bias conditions at DC.
2Device complexity
If conventional voltage follower architecture is used, then the circuit is simple, but linearity is poor and harmonic waves are not suppressed
Solution Approach 1:
The patent transforms the impedance characteristic from static to dynamic by introducing frequency dependence through a capacitor. This creates a frequency-dependent impedance that selectively affects different frequency components, suppressing harmonics while passing the fundamental signal with high fidelity.
3Manufacturing precision
If resistors are used for impedance transformation, then the circuit can transform resistance, but the transformation is not effective across all frequencies particularly at low frequencies
Solution Approach 1:
The patent changes the impedance parameter from constant to frequency-dependent by adding a capacitor in parallel with the resistor. This creates an impedance that varies with frequency, enabling effective resistance transformation across a broad frequency range including low frequencies, where conventional resistors fail.
Data Source
AI summary
An input buffer using a frequency dependent impedance circuit to compensate for nonlinearity in low frequency is shown. In a pseudo-differential architecture, a frequency-dependent impedance circuit is coupled between the drain of a positive input transistor of the flipped voltage follower and the drain of a negative input transistor of the flipped voltage follower. In a single-ended architecture, the frequency-dependent impedance circuit is coupled between the drain of an input transistor of the flipped voltage follower and an alternating current ground. The frequency-dependent impedance circuit includes a capacitor.