Dynamic Current Mirror Using Miller Capacitance for Current Matching
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Solution Overview
Problem
Traditional current mirrors require precise matching of transistors for accurate current replication, are susceptible to transistor variation, and cannot handle time-varying currents or sample-and-hold signals, limiting their integration and functionality in larger chips.
Innovation Solution
A dynamic current mirror (DCM) operates in two stages, using a current memory cell and an inverting voltage amplifier with Miller-effect amplification to store and replicate input currents, eliminating the need for precise transistor matching and enabling integration on larger chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current mirrors use two transistors with precise size matching to achieve accurate current replication, then current matching precision is improved, but device area increases and manufacturing precision requirements worsen due to unintentional variation across integrated chips
Solution Approach 1:
The patent extracts the current mirror functionality from the traditional two-transistor configuration into a single-transistor dynamic current mirror with a memory cell. The memory cell stores the input current information, allowing the output transistor to replicate the current without requiring precise matching with the input transistor, thus eliminating the manufacturing precision constraint while maintaining current matching accuracy
Solution Approach 2:
Instead of directly copying current through matched transistors, the patent uses a memory cell to store the input current information and then retrieves it to drive the output transistor. This indirect copying method through storage eliminates the need for precise transistor matching while achieving accurate current replication
2Stability of the object's composition
If traditional current mirrors are designed as continuous time circuits to maintain constant output current, then current stability is improved, but adaptability to time-varying currents and sample-and-hold operations deteriorates
Solution Approach 1:
The patent transforms the static continuous-time current mirror into a dynamic circuit that can operate in different modes. The memory cell enables the circuit to switch between tracking mode (for time-varying currents) and hold mode (for sample-and-hold operations), providing both stability when needed and adaptability when required
Solution Approach 2:
The dynamic current mirror uses periodic sampling of the input current into the memory cell, followed by periodic retrieval to drive the output. This periodic action allows the circuit to handle time-varying currents by capturing snapshots at specific intervals while maintaining stability during the hold phase
3Measurement precision
If transistor size is increased to achieve desired performance in traditional current mirrors, then current matching precision is improved, but integrated chip area increases
Solution Approach 1:
The patent extracts the current storage function into a separate memory cell, allowing the use of smaller transistors for current mirroring. The memory cell assumes the burden of maintaining current information, enabling the use of compact transistors that occupy less chip area while still achieving precise current replication through the stored information
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 DCM effectively replicates input currents without transistor matching, reducing performance degradation and allowing integration on larger chips, while supporting time-varying currents and sample-and-hold operations.
Implementation Method 1
The inverting amplifier is configured to invert and amplify an input voltage associated with the input signal such that a capacitance of a feedback capacitive element of the circuit is increased via a Miller-effect amplification
Implementation Method 2
During the first operational stage, the cell capacitance is configured to store the input voltage
Implementation Method 3
During the second operational stage, the cell capacitance is configured to provide the stored input voltage to drive the transmission of the output signal
Data Source
AI summary
According to aspects of the present disclosure, a dynamic current mirror (DCM) is operated in a first stage and a second stage that is temporally subsequent to the first stage. The DCM includes a current memory cell and an inverting voltage amplifier. During the first stage, the current memory cell receives an input current and stores a corresponding voltage via a capacitance of the current memory cell. During the second stage, the current memory cell employs the stored input voltage to drive an output current that matches the input current. The inverting voltage amplifier is employed to increase the capacitance of the current memory cell via a Miller-effect amplification of the capacitance.