Differential TX Circuit Harvesting RX Supply for Low-Power Links

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional data transmitter circuits face challenges in reducing power consumption while maintaining speed and efficiency, particularly due to the high power consumption of the receiver circuit, which is three to four times that of the transmitter circuit, and existing techniques either increase capacitance, reduce speed, or lead to substantial power consumption in the driver circuit.

Innovation Solution

A transmitter circuit design that draws current from the receiver circuit's power supply through a differential channel, with a driver circuit coupled across resistors and a pre-driver circuit powered from the common mode voltage node, reducing dynamic leakage and increasing speed by stabilizing voltage at the common mode node.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the pre-driver circuit uses an external 1V core power supply, then power consumption by the pre-driver circuit is reduced, but the differential switching pair area and current source area in the driver circuit increase due to limited headroom

Engineering Contradiction:

Improvepower consumptionVSAvoiddifferential switching pair area

Core Design Contradiction:

Use of energy by moving objectVSArea of moving object

Solution Approach 1:

The patent merges the pre-driver circuit and driver circuit into a single integrated structure where the pre-driver is directly coupled to the driver without external power supply connections. This integration allows the pre-driver to operate from the same power supply node as the driver, eliminating the need for separate 1V core power supply and its associated area overhead for level shifting and isolation circuitry.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The common power supply node serves multiple functions: it provides power to both the pre-driver and driver circuits, acts as a reference voltage, and enables direct signal coupling between stages. This multi-functionality reduces the overall circuit area by eliminating dedicated power supply paths and level shifting circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Use of energy by moving object

If the pre-driver circuit uses an external 1V core power supply, then power consumption is reduced, but the speed of operation decreases due to large capacitance on the input and common source node

Engineering Contradiction:

Improvepower consumptionVSAvoidspeed of operation

Core Design Contradiction:

Use of energy by moving objectVSSpeed

Solution Approach 1:

By merging the pre-driver and driver circuits into a unified structure with a shared power supply node, the patent eliminates the large capacitance that would otherwise be required on isolated input nodes. The direct coupling between pre-driver and driver stages reduces the total capacitance seen by the switching nodes, thereby improving speed of operation.

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If the common source node is used as power supply for pre-driver circuit, then power consumption is reduced, but the output impedance of the current source degrades due to added capacitance

Engineering Contradiction:

Improvepower consumptionVSAvoidoutput impedance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent segments the current source function from the power supply function. The current source is implemented as a dedicated circuit block with high output impedance that is separate from the power supply node. The pre-driver circuit draws power from the common node but its signal path is isolated through the high-impedance current source, preventing capacitance loading from degrading the current source performance.

Inventive Principle:

Principle #1Segmentation

4Reliability

If external 3.3V power supply is used to provide sufficient margin on the driver circuit, then headroom is sufficient, but power consumption increases substantially

Engineering Contradiction:

Improveheadroom marginVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the voltage level parameters by operating the entire transmitter circuit, including both pre-driver and driver stages, from a single low-voltage power supply node. This parameter change is compensated by optimizing the transistor sizing and biasing conditions to ensure sufficient headroom for signal swing, thereby achieving reliable operation without the substantial power consumption associated with 3.3V operation.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10069637B2Transmitter circuit harvesting power from power supply of a receiver circuit

Publication Date: 2018.09.04 LATTICE SEMICON CORP

AI summary

A transmitter (TX) circuit harvesting power from a power supply of a receiver (RX) circuit is disclosed herein. The TX circuit for data transmission over a differential channel comprises a driver circuit coupled with the differential channel across a first pair of resistors. One terminal of each resistor of the first pair coupled together at a common mode voltage node. The differential channel is series terminated at the RX circuit by a second pair of resistors to a power supply node of the RX circuit. The driver circuit includes a differential pair and a current source drawing current from the power supply node of the RX circuit. A pre-driver circuit coupled with the driver circuit provides an output of the pre-driver circuit as an input to the driver circuit. At least the pre-driver circuit is powered from the common mode voltage node of the driver circuit.