Differential LNA Circuit Without Baluns for Low-Noise Conversion
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Solution Overview
Problem
Conventional single-ended input to differential-ended output amplifier circuits face challenges in reducing die size and noise interference, with existing solutions either increasing chip cost or requiring large die area due to additional components.
Innovation Solution
A single-ended input to differential-ended output amplifier circuit that incorporates a single-ended to differential-ended converter with a specific transistor and capacitor configuration, eliminating the need for external baluns and inductive transformers, thereby reducing die size and noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a balun is added outside the chip to convert single-ended input to differential-ended output, then signal conversion is achieved, but chip cost increases and device complexity increases
Solution Approach 1:
The patent integrates the single-ended to differential-ended conversion function directly into the amplifier circuit by using the amplifier's own output terminals and internal components (capacitors and resistors) to perform the conversion. This merging of functions eliminates the need for external baluns and reduces overall device complexity while maintaining signal conversion capability.
Solution Approach 2:
The amplifier circuit is designed to perform multiple functions: it amplifies the input signal and simultaneously converts single-ended input to differential-ended output. The output terminals serve dual purposes as both amplification outputs and conversion circuit inputs, making the amplifier a multi-functional component that reduces the need for separate dedicated conversion components.
2Adaptability or versatility
If a single-ended input to differential-ended output inductive transformer is added to the chip, then differential-ended output is achieved, but die area increases
Solution Approach 1:
The conversion circuit uses the amplifier's existing output terminals and internal components (capacitors C1-C4 and resistors R1-R4) to perform differential conversion. By merging the conversion function into the existing amplifier structure rather than adding separate inductive transformers, the patent significantly reduces the required die area while achieving the same differential output capability.
Solution Approach 2:
The patent extracts the essential conversion function from the bulky inductive transformer and implements it using smaller discrete components (capacitors and resistors) within the amplifier circuit. This extraction of the core functionality from its traditional bulky implementation reduces the die area requirement.
3Device complexity
If a conventional differential amplifier pair with grounded negative terminal is used, then circuit simplification is achieved, but noise coupling from substrate increases
Solution Approach 1:
The patent introduces floating capacitors C1 and C2 as intermediary elements that couple the amplifier outputs to the conversion circuit inputs without direct substrate connection. These intermediary capacitors block noise coupling from the substrate while still allowing the simplified differential amplifier structure to function, thus resolving the contradiction between circuit simplification and noise reduction.
Solution Approach 2:
The patent extracts the noise coupling path from the circuit by removing the direct grounded connection and replacing it with floating capacitive coupling. This extraction of the harmful noise path while maintaining the simplified amplifier structure allows the circuit to achieve both low complexity and low noise coupling.
Data Source
AI summary
A single-ended input to differential-ended output amplifier circuit comprises an amplifier for amplifying an input signal into an amplified signal comprises an input for receiving the input signal; and a first input and a single-ended input to differential-ended output conversion circuit to convert the amplified signal to a differential signal pair, comprising a first transistor for receiving the amplified signal having a first gate coupled to the first output, a first first terminal coupled to a second output, and a first second terminal coupled to a first node; a second transistor having a second gate, a second first terminal coupled to a third input, and a second second terminal coupled to the first node; a second capacitor coupled between the second output and the second gate; a first and a second resistors and the voltage source; and a current source coupled between the first node and a ground.