Voltage Level Shifter With Cross-Coupled Load Chain
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Solution Overview
Problem
Existing voltage level shifters face inefficiencies due to high DC power consumption and signal transition delays, limiting their frequency range and requiring complex schemes with high device counts, which complicates AC signal propagation and increases area on the chip.
Innovation Solution
A voltage level shifting circuit with a cross-coupled load chain transistor pair and regulated current sources, operated in conjunction with a reference generator, reduces DC current consumption and minimizes signal transition delays by optimizing current levels in load devices, even at small AC signal voltage swings, and uses source followers as input buffers to reduce device count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a voltage level shifter uses a conventional input transistor pair and load chain, then voltage level shifting is achieved, but DC power consumption increases
Solution Approach 1:
The patent implements a dynamic biasing scheme where the load chain transistor is periodically switched between active and cutoff states based on the input signal phase. During one phase, the load chain transistor is active to enable signal transmission, while during the other phase, it is in cutoff to minimize DC power consumption. This periodic action allows the circuit to achieve both low power consumption and reliable signal transition.
2Productivity
If signal transition speed is increased, then frequency range is improved, but signal transition delays increase
Solution Approach 1:
The patent employs dynamic biasing of the load chain transistor that adapts to the input signal conditions. The transistor's operating point is dynamically adjusted to optimize the trade-off between transition speed and delay. By controlling the gate voltage of the load chain transistor based on the differential input signal, the circuit achieves faster transition times while maintaining signal integrity across a wider frequency range.
Solution Approach 2:
The differential configuration provides inherent feedback mechanisms where the state of one transistor influences the other through the common current source. This feedback helps in achieving balanced and controlled signal transitions, reducing delays while maintaining the ability to operate at higher frequencies. The cross-coupling effect in the differential pair provides regenerative action that speeds up transitions.
3Reliability
If device count is increased to improve voltage level shifting performance, then shifting capability is enhanced, but circuit complexity increases
Solution Approach 1:
The patent achieves multiple functions using a minimal set of devices. The differential input transistor pair serves both as the voltage level shifting element and as the signal amplification stage. The dynamic load chain transistor provides both biasing control and signal transmission functions. This multi-functionality reduces the overall device count while maintaining robust voltage level shifting capability across different voltage domains.
Solution Approach 2:
The patent combines the voltage level shifting function with the signal buffering function in a single stage. The differential pair inherently provides both voltage translation and signal regeneration, eliminating the need for separate buffering stages. The load chain transistor is integrated into the same circuit block, providing both current sourcing and signal path functions, thereby reducing total device count and simplifying the circuit architecture.
Data Source
AI summary
A voltage level shifter with an input transistor pair, a cross-coupled load chain transistor pair and a pair of current sources, effects reduced power consumption through the use of the cross-coupled load chain transistor pair to minimize the DC current component present in known voltage level shifters. In specific embodiments, feedback elements may be used to minimize delays in signal transitions. A reference voltage that corresponds to a current capability of the input transistor pair may be used to regulate the current sources in the load chain. Changes in a swing of the input signal voltage received by the input transistor pair may be reflected in corresponding changes to the reference voltage. The voltage level shifter may be of particular use in a buffer.