Digitally Controlled Grounded Capacitor Multiplier for IC Area Limits
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Solution Overview
Problem
Integrated circuits (ICs) face constraints that limit practical capacitors to low capacitance levels, making it challenging to achieve higher capacitance values necessary for electronic circuits, particularly for filters and timing circuits.
Innovation Solution
A digitally controlled grounded capacitance multiplier circuit using an operational amplifier, a digitally controlled current amplifier, and resistors to amplify input current based on digital control signals, allowing for programmable equivalent capacitance values through resistor ratios and amplifier gain, achieving large multiplication factors with only two active devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If practical capacitors are used in integrated circuits, then the circuit can store electrical energy, but the capacitance value is limited to relatively low levels due to area constraints
Solution Approach 1:
The patent introduces an operational amplifier and resistor network as intermediary components between the input node and ground. This active circuit configuration acts as a mediator that synthesizes a virtual capacitor with equivalent capacitance Ceq = C × (1 + R1/R2), where C is the physical capacitor value and R1/R2 are resistor ratios. This intermediary active circuit enables achieving high equivalent capacitance values without requiring proportionally large physical capacitor areas, thus resolving the contradiction between capacitance value and area consumption.
2Quantity of substance
If a capacitance multiplier circuit is used to increase capacitance value, then higher equivalent capacitance is achieved, but the circuit complexity increases
Solution Approach 1:
The operational amplifier in the patent serves multiple functions simultaneously: it acts as a voltage buffer, creates a virtual ground at the inverting input, enables the capacitance multiplication through feedback, and provides high input impedance. By making the op-amp multi-functional, the circuit achieves high equivalent capacitance without requiring additional dedicated components for each function, thus minimizing circuit complexity while maximizing capacitance multiplication capability.
Solution Approach 2:
The patent achieves variable equivalent capacitance by changing the resistor ratio R1/R2 in the feedback network. Since capacitance Ceq = C × (1 + R1/R2), adjusting the resistor values allows continuous tuning of the equivalent capacitance parameter without changing the physical capacitor C or adding complex switching networks. This parameter change approach simplifies the circuit compared to using multiple capacitors or complex digital control mechanisms.
3Ease of manufacture
If fixed capacitance values are used in ICs, then manufacturing is simplified, but adaptability to different circuit requirements is reduced
Solution Approach 1:
The patent transforms the fixed capacitance into a dynamic, adjustable parameter by incorporating the op-amp based capacitance multiplier circuit. The equivalent capacitance Ceq = C × (1 + R1/R2) can be dynamically adjusted by changing the resistor ratio R1/R2, allowing the same physical capacitor C to provide different effective capacitance values. This dynamic configuration enables a single IC design to adapt to different circuit requirements without requiring multiple fixed-capacitance variants, thus improving versatility while maintaining manufacturing simplicity.
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 solution enables the creation of integrated circuits with higher capacitance values, reducing circuit size, enhancing performance, and providing cost-effectiveness by allowing digital tuning of filter parameters, thus overcoming the limitations of low capacitance in ICs.
Implementation Method 1
a first operational amplifier (op-amp) having at least a first input terminal, an output terminal, and a second input terminal that is grounded. The circuit also comprises a reference capacitor connected in series between the input node and the first input terminal of the first op-amp. Additionally, the circuit comprises a first resistor arranged in a feedback loop connecting the output of the first op-amp to the first input terminal
Implementation Method 2
a digitally controlled current amplifier (DCCA) having an analog input terminal for receiving an input current, an output terminal and a digital input terminal for receiving a digital control signal. The DCCA is configured to generate an output current by amplifying the input current as a function of the digital control signal
Data Source
AI summary
A digitally controlled grounded capacitor multiplier includes: a single capacitor directly connected at one end to an input voltage and at another end to a negative input of an operational amplifier; the operational amplifier including a negative feedback loop; and a digitally controlled current amplifier (DCCA) connected to an output of the operational amplifier. The DCCA digitally controls the digitally controlled grounded capacitor multiplier. The digitally controlled grounded capacitor multiplier comprises only two active devices consisting of the operational amplifier and the DCCA.