Differential PLL Filter Circuit With Effective Capacitance Multiplication
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Solution Overview
Problem
In the semiconductor industry, phase locked loop filters with large capacitors occupy significant space and increase costs, while also causing non-linear signal variations.
Innovation Solution
A differential filter circuit design utilizing transconductance amplifiers and capacitors, where the larger transconductance of one amplifier results in an effective capacitor multiplication effect, allowing for smaller actual capacitance values and reduced physical size, while maintaining larger capacitance values, and using two capacitors connected to each input of the amplifiers for improved linearity and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitors are used in the filter, then the filtering performance is improved, but the physical size and cost increase
Solution Approach 1:
The patent changes the electrical parameters by using transconductance amplifiers with different gain values to create an equivalent capacitance effect. The differential amplifier converts voltage signals to current signals, and the combination of capacitors with different values (C1, C2, C3, C4) and amplifier gains creates an effective capacitance that mimics a larger capacitor without requiring the physical space of a large actual capacitor.
2Reliability
If large capacitors are used in the filter, then the filtering performance is improved, but the manufacturing cost increases
Solution Approach 1:
The patent uses parameter transformation by converting the capacitance requirement into an equivalent electrical behavior through transconductance amplifiers. Instead of manufacturing and placing a large physical capacitor, the design uses smaller capacitors combined with amplifier circuits that provide the equivalent filtering effect, thereby reducing component costs and manufacturing complexity.
3Reliability
If large capacitors are used in the filter, then the capacitance value is sufficient, but the signal linearity deteriorates
Solution Approach 1:
The patent segments the single large capacitor function into multiple smaller capacitors (C1, C2, C3, C4) distributed across different amplifier stages. This segmentation allows each capacitor to operate within its linear range while the overall circuit maintains the required total capacitance effect, thereby improving signal linearity while achieving sufficient effective capacitance.
4Area of stationary object
If smaller capacitors are used to reduce size, then the physical area is reduced, but the effective capacitance value decreases
Solution Approach 1:
The patent introduces transconductance amplifiers as intermediary elements between the small physical capacitors and the filtering function. These amplifiers multiply the effective capacitance by converting voltage to current and back, creating a virtual capacitance effect that is larger than the physical capacitors, thus bridging the gap between small physical size and large effective capacitance.
Data Source
AI summary
In one embodiment, a filter circuit is formed to include a transconductance amplifier. The filter circuit has one pair of capacitors connected between at least one input of the amplifier and an input signal that is to be filtered.