Wideband LNA DC Loops With Back-Gate Bias to Eliminate AC Coupling
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Solution Overview
Problem
Conventional AC coupling capacitors consume significant chip area and impair performance in wideband low noise amplifiers (LNAs), especially at lower frequencies, due to increased resistance which decreases performance.
Innovation Solution
The use of DC loops with back gate biased transistors eliminates AC coupling capacitors, employing three DC coupled inverter-based amplifying stages with feedback loops and bias circuitry to provide complementary output currents and cancel noise and distortion, utilizing fully depleted silicon-on-insulator (FDSOI) transistors for efficient biasing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC coupling capacitors are used to isolate DC bias settings, then DC isolation is achieved, but chip area increases significantly
Solution Approach 1:
The patent extracts and removes the AC coupling capacitor from the LNA circuit, replacing it with a DC coupling scheme. This eliminates the need for large capacitors while maintaining signal coupling functionality through direct DC connection between stages, thereby reducing chip area significantly.
Solution Approach 2:
The patent introduces an intermediary mechanism (DC coupling with bias isolation through circuit topology) that allows both DC connection for signal coupling and DC bias isolation to be achieved simultaneously, replacing the traditional capacitor-based approach.
2Reliability
If AC coupling capacitors are used to block DC, then DC isolation is achieved, but performance deteriorates at lower frequencies due to increased resistance
Solution Approach 1:
By removing the AC coupling capacitor entirely, the patent eliminates the frequency-dependent resistance issue that degrades LNA performance at lower frequencies (500 MHz), allowing consistent performance across the entire wideband operating range.
Solution Approach 2:
The DC coupling scheme provides continuous signal coupling without the intermittent blocking effect of capacitors, ensuring uninterrupted signal transmission and consistent performance across all frequencies from 500 MHz to 3 GHz.
3Manufacturing precision
If three DC coupled inverter-based amplifying stages with feedback loops are used, then noise and distortion are cancelled, but device complexity increases
Solution Approach 1:
The patent segments the LNA into three distinct inverter-based amplifying stages, each with its own feedback loop. This segmentation allows independent optimization of each stage and enables noise and distortion cancellation through the complementary output currents from the third stage.
Solution Approach 2:
Each inverter stage incorporates a feedback loop that feeds a portion of the output signal back to the input, enabling precise control of gain and impedance matching while canceling noise and distortion through the complementary signal paths.
Data Source
AI summary
Methods form amplifier device structures that include first-third amplifier devices. The first amplifier device produces an intermediate signal. The second amplifier device is connected to an input of the first amplifier device and produces an amplified inverted output signal. The third amplifier device inverts the intermediate signal to produce an amplified non-inverted output signal that is complementary to the amplified inverted output signal. A resistor feedback loop is connected to the input and output of the first amplifier device. A gain ratio of the gain of the third amplifier device to the gain of the second amplifier device matches a resistance ratio of the source resistance of the input signal to the resistance of the resistor added to the source resistance. Also, DC loop circuits are connected to the first-third amplifier devices, and each of the DC loop circuits connects an amplifier device output to an amplifier device input.