Split-Band Baseband Amplifier for Bandwidth Beyond fmax/2
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Solution Overview
Problem
Existing distribution-type baseband amplifiers are limited in bandwidth to about 1/2 of the maximum oscillation frequency of the transistors, making it difficult to achieve significant increases beyond this limit.
Innovation Solution
A baseband amplifier configuration that includes a distributed amplifier, an RF amplifier with higher frequency characteristics, a demultiplexer, and a multiplexer to split and combine signals based on frequency cutoffs, allowing for broader bandwidth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a distribution-type baseband amplifier is used with transistors having maximum oscillation frequency fmax, then the amplifier can operate with a bandwidth of about fmax/2, but the bandwidth cannot be significantly increased beyond this limit
Solution Approach 1:
The broadband amplifier is segmented into multiple functional blocks: a distributed amplifier block for high-frequency signals (above fmax/2) and a baseband amplifier block for low-frequency signals (below fmax/2). The demultiplexer divides the input signal into these frequency bands, and the multiplexer combines the amplified outputs. This segmentation allows each block to be optimized for its specific frequency range, achieving total bandwidth exceeding fmax while maintaining manageable complexity in each individual block.
2Adaptability or versatility
If the characteristic impedance of transmission lines is designed to be 50 Ω incorporating parasitic capacitance of transistors, then connection to external devices is established, but the cutoff frequency of the pseudo transmission lines limits the achievable bandwidth
Solution Approach 1:
The demultiplexer acts as an intermediary that separates the broadband input signal into two frequency bands before they enter the respective amplifier blocks. By introducing this intermediary component, the system can handle frequencies both above and below the distributed amplifier's cutoff frequency (fmax/2), effectively extending the overall bandwidth beyond what a single distributed amplifier could achieve while maintaining 50 Ω compatibility through proper impedance design in each block.
Data Source
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Figure 2B
AI summary
A baseband amplifier includes: a distributed amplifier (10); an RF amplifier (11) that has a higher frequency transmission characteristic than the distributed amplifier (10); a demultiplexer (12) that outputs, to the distributed amplifier (10), a signal that includes at least a signal component of equal to or less than a high-frequency-side cutoff frequency of the distributed amplifier (10) in an input signal and outputs, to the RF amplifier (11), a signal that includes at least a signal component of equal to or greater than a low-frequency-side cutoff frequency of the RF amplifier (11) in the input signal; and a multiplexer (13) that multiplexes a signal amplified by the distributed amplifier (10) and a signal amplified by the RF amplifier (12).