Always-On Implant Receiver with Antiphase Offset Correction
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Solution Overview
Problem
Traditional differential amplifiers are not suitable for detecting low amplitude implant-to-implant communication signals due to high input offset voltage and susceptibility to drift, which can lead to synchronization issues in dual chamber pacemaker systems.
Innovation Solution
The use of a pair of auto-zeroed differential amplifiers that are selectively enabled and offset corrected in antiphase, allowing for continuous monitoring of low frequency wakeup signals while minimizing power consumption, and enabling a high frequency receiver only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional differential amplifier is used to receive implant-to-implant communication signals, then the receiver structure is simple, but the input offset voltage is greater than 1mV (typically 10mV or more) which exceeds the low amplitude of received signals, making detection impossible
Solution Approach 1:
The receiver is divided into multiple differential amplifiers (first and second differential amplifiers) that operate in different phases. One amplifier performs offset correction while the other monitors for incoming signals, and vice versa. This segmentation allows the system to achieve both low offset voltage and continuous signal monitoring capability.
Solution Approach 2:
The differential amplifiers alternately perform offset correction and signal monitoring in periodic phases. During each cycle, one amplifier is in offset correction phase while the other is in signal monitoring phase, creating a periodic switching pattern that ensures continuous monitoring capability while maintaining low offset voltage through regular correction cycles.
2Measurement precision
If offset correction is performed continuously to remove input offset voltage drift, then measurement precision is improved, but the receiver becomes blind to incoming signals during correction phases, causing synchronization loss
Solution Approach 1:
The receiver functionality is segmented across multiple differential amplifiers, allowing one amplifier to perform offset correction while another simultaneously performs signal monitoring. This segmentation eliminates the blind period problem by ensuring that at least one amplifier is always in signal monitoring phase.
Solution Approach 2:
Offset correction is performed in advance during dedicated correction phases before signal monitoring begins. By completing offset correction beforehand and then switching to monitoring mode, the system prepares the amplifiers in advance so that when monitoring starts, the offset voltage is already minimized, enabling both functions to coexist without interference.
3Reliability
If the receiver is always on to monitor for implant-to-implant signals, then signal detection reliability is improved, but power consumption increases significantly draining the battery
Solution Approach 1:
The differential amplifiers operate in periodic cycles, alternating between offset correction phase and signal monitoring phase. During offset correction phase, the amplifier consumes power for correction operations, but during signal monitoring phase, it consumes minimal power while remaining ready to detect signals. This periodic operation reduces average power consumption compared to continuous full-power operation.
Solution Approach 2:
The receiver system dynamically switches between different operational states (offset correction mode and signal monitoring mode) based on timing signals. This dynamic state switching allows the system to optimize power consumption by being active only when necessary for each function, rather than maintaining constant high-power operation.
Data Source
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AI summary
Disclosed herein are implantable medical devices (IMDs) including a receiver and a battery, and methods for use therewith. The receiver includes first and second differential amplifiers, each of which monitors for a predetermined signal within a frequency range and drains power from the battery while enabled, and while not enabled drains substantially no power from the battery. To remove undesirable input offset voltages, each of the differential amplifiers, while enabled, is selectively put into an offset correction phase during which time the predetermined signal is not detectable by the differential amplifier. At any given time at least one of the first and second differential amplifiers is enabled without being in the offset correction phase so that at least one of the differential amplifiers is always monitoring for the predetermined signal. In this manner, the receiver is never blind to signals, including the predetermined signals, sent by another IMD.