On-Chip Reference Voltage Filtering for Mobile Phone Supply Noise
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Solution Overview
Problem
Existing mixed-signal integrated circuits require external capacitors for filtering, which add pads and pins to chips, increase area and cost, and do not effectively address interference in supply voltages, especially in mobile phones with fluctuating battery-supplied voltages.
Innovation Solution
An on-chip filter apparatus using a differential filtering resistive element with PMOS and NMOS current mirrors and an on-chip filter capacitor to provide a filtered output voltage, eliminating the need for external capacitors and effectively tracking changes in supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external filter capacitors are used to suppress interferences, then filtering performance is improved, but chip area and package complexity increase due to additional pads and pins
Solution Approach 1:
The patent combines the filter capacitor function with existing on-chip structures by utilizing the bond pad capacitance and integrating capacitor structures directly on the chip. This merging eliminates the need for separate external filter capacitors and their associated pads and pins, thereby maintaining filtering performance while reducing package complexity
Solution Approach 2:
The patent extracts the filtering function from external components and relocates it to on-chip structures. By taking out the dependency on external filter capacitors and implementing filtering using on-chip capacitor structures and bond pad capacitance, the solution eliminates additional pads and pins while preserving the interference suppression capability
2Reliability
If external filter capacitors are used for voltage filtering, then interference suppression is improved, but manufacturing cost increases due to additional components
Solution Approach 1:
The patent merges the filtering function with on-chip structures, eliminating the need for separate external filter capacitor components. This reduces the bill of materials and assembly complexity, thereby lowering manufacturing cost while maintaining interference suppression performance
Solution Approach 2:
The patent extracts the filtering function from external components and implements it using on-chip capacitor structures. This eliminates the need to purchase and assemble external filter capacitors, reducing both component cost and assembly cost
3Device complexity
If only PMOS transistors are used in the current mirror circuit, then circuit simplicity is maintained, but the circuit can only charge the capacitor leading to rising voltage under interference
Solution Approach 1:
The patent introduces asymmetry into the current mirror circuit by using different transistor types (PMOS and NMOS) for charging and discharging functions. This asymmetric design allows the circuit to perform both charge and discharge operations, enabling proper filtering action while maintaining reasonable circuit simplicity
Solution Approach 2:
The patent inverts the conventional approach by using NMOS transistors for the discharge function instead of relying solely on PMOS transistors for charging. This inversion enables the capacitor to be discharged during interference conditions, preventing voltage rise and improving voltage stability
4Device complexity
If on-chip filtering is implemented without external capacitors, then area and cost are reduced, but filtering effectiveness must be maintained
Solution Approach 1:
The patent makes the bond pad serve multiple functions: it acts as both a connection point for power or signal and as a capacitor structure for filtering. This multi-functionality eliminates the need for separate external filter capacitors while maintaining filtering effectiveness
Solution Approach 2:
The patent enables the on-chip structures to provide their own filtering capability without requiring external assistance. The integrated capacitor structures and current mirror circuits work together to provide effective filtering, making the system self-sufficient
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The on-chip filter apparatus reduces the impact of supply voltage fluctuations and interferences, achieving cost savings and improved filtering performance without external capacitors, while maintaining a stable output voltage even during burst transmissions in mobile phones.
Implementation Method 1
A filter capacitor is situated at the output side of the apparatus. It is connected between the common output node and ground.
Data Source
AI summary
Apparatus (40) comprising a voltage input (49) for applying an unfiltered voltage (V_unfil) and a current input (48) for receiving a bias current (Ib) from a current source. The apparatus (40) further comprises a differential filtering resistive circuit with a first current mirror (44) and a second current mirror (43), being situated between a common output node (50) and said voltage input (49). A first mirror circuit (42) for mirroring the bias current (Ib) to said first current mirror (44), and a second mirror circuit (41) for mirroring a current (Ix) to said second current mirror (43) are employed. A filter capacitor (51) situated at the output side of the apparatus (40), said filter capacitor (51) being connected on one side to said common output node (50) and on the other side to ground. The apparatus (40) provides a filtered output voltage (V_fil) at said common output node (50).