Active CMOS Termination Circuit for Low-Power High-Bandwidth I/O
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Solution Overview
Problem
The increasing demand for high-performance, low-power semiconductor memory devices is hindered by the limitations of parasitic capacitance in wire-bond and electronic packages, which restrict bandwidth and lead to increased power consumption when using lower impedance receiver termination.
Innovation Solution
An active low-power termination (ALPT) circuit using CMOS active devices with multi-modes of impedance, featuring a push-pull configuration and a feed-forward mechanism to manage impedance during logic transitions, allowing for programmable impedance and temperature compensation, reducing power consumption while maintaining high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If lower impedance receiver termination is used to increase bandwidth, then bandwidth is improved, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the termination impedance variable rather than fixed. The circuit dynamically adjusts impedance based on signal transition states: during transitions it maintains low impedance for bandwidth, while in steady states it switches to high impedance for low power. This is achieved through the push-pull amplifier configuration that can operate in different modes depending on the input signal state.
Solution Approach 2:
The patent changes the impedance parameter dynamically based on operating conditions. The termination circuit switches between high and low impedance states depending on whether the signal is in transition or steady state. This parameter change is controlled by detecting the differential voltage between input signals and adjusting the termination accordingly, allowing optimization of both bandwidth and power consumption at different times.
2Device complexity
If passive resistive termination is used to simplify the circuit, then device complexity is reduced, but power consumption increases
Solution Approach 1:
The patent replaces static passive resistive termination with a dynamic active circuit that changes its characteristics based on signal state. The push-pull amplifier configuration allows the circuit to actively switch between high-impedance (low power) and low-impedance (high bandwidth) modes, providing the benefits of complex active control only when necessary for performance.
Solution Approach 2:
The termination circuit operates in periodic cycles, alternating between high-impedance steady-state mode and low-impedance transition mode. The feed-forward mechanism detects upcoming transitions and pre-adjusts the termination, creating a rhythmic pattern of impedance changes that optimizes power consumption while maintaining signal integrity during transitions.
3Use of energy by moving object
If higher impedance receiver termination is used to reduce power consumption, then power consumption is reduced, but bandwidth is limited
Solution Approach 1:
The patent resolves this contradiction by making impedance dynamic rather than static. The circuit maintains high impedance during steady states to minimize power consumption, but automatically switches to low impedance during signal transitions to maximize bandwidth. This dynamic adaptation allows the system to achieve both low power and high performance at different appropriate times.
Solution Approach 2:
The feed-forward mechanism in the patent performs preliminary action by detecting the differential voltage between input signals before the actual transition occurs. This allows the termination circuit to pre-adjust its impedance state in preparation for an upcoming transition, ensuring that low impedance is already in place when the transition occurs, thereby maximizing bandwidth without requiring continuous low impedance.
Data Source
AI summary
An active low-power termination circuit includes a first leg of a pair of transistors connected in series between the high supply level and ground, where the termination input is at a node between the transistors of the first node. A second leg uses a feed forward mechanism to control the voltage levels on the control gates of the transistors of the first leg. The second leg includes a second pair diode connected transistors, each of which is has its control gate connected to the control gate of the corresponding transistor in the first leg. A variable current source connected in series with the transistors of the second leg and is controlled by the output of a difference amplifier that has one input connect to an intermediate node of the second leg and a second input connected to a reference level intermediate to the high supply level and ground.