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![(a) Block diagram of the wireless pressure sensor IC showing selective power gating switches used to limit power consumption of telemetry and instrumentation circuits. The schematic of (b) shows the individual circuits within the always-running power management unit (after [4] ).](profile/Steve-Majerus-3/publication/261153310/figure/fig1/AS:296946410508288@1447808949380/a-Block-diagram-of-the-wireless-pressure-sensor-IC-showing-selective-power-gating.png)
(a) Block diagram of the wireless pressure sensor IC showing selective power gating switches used to limit power consumption of telemetry and instrumentation circuits. The schematic of (b) shows the individual circuits within the always-running power management unit (after [4] ).
Source publication
A custom IC for wireless bladder pressure sensing incorporates power-management circuitry to limit the active time of the instrumentation circuitry and to minimize telemetry rate. Instrumentation circuits are operated with low duty factors in a pipelined manner to generate 100-Hz pressure samples. Telemetry rate is adapted according to sample activ...
Citations
... The offset removal system was combined as part of a wireless bladder pressure sensing ASIC fabricated in OnSemi C5F 0.5-μm (Fig. 6) [9]. The IDAC and digital components of the cancellation system consumed 0.3 mm 2 . ...
Implanted pressure sensors suffer from long-term offset drift due to atmospheric changes, package moisture absorption, and patient factors such as posture, implant shift, and tissue overgrowth. Traditionally, wide dynamic range instrumentation is used to satisfy the full-scale and sensitivity requirements for a given application. Transmission of extra bits greatly increases the power draw of an implanted medical device, and simple AC-coupling cannot monitor static pressures. We present a mixed-signal offset cancellation loop to maximize the AC dynamic range of instrumentation circuitry. A digital implementation allows for designer control of the cancellation system time constant and was specifically designed for power-gated pressure sensors. Pressure offset is calculated by digital integration and a bipolar IDAC with coarse/fine tuning injects an offset-cancelling current into a standard piezoresistive MEMS pressure sensor. Test results showed a dynamic range increase of 2.9 bits using dynamic offset cancellation, for an effective sensing range of 11 bits using 8-bit instrumentation. The measured step response of the system showed an overall highpass response of 2.3–3.8 mHz. This approach is therefore relevant for bio-sensing of pressures in organs with a very slow physiologic response, e.g. the bladder.
... We adopted a highly-integrated approach to the pressure monitor, which consists of a custom integrated circuit, MEMS absolute pressure sensor [6], rechargeable battery, and discrete inductive antennas for wireless charging and data telemetry (Fig. 2). To reduce the implant battery size, the pressure monitor ASIC was designed with three charge-maintaining strategies: ultra-low-power instrumentation and adaptive rate telemetry [7], long-range RF wireless charging, and a sub-nA standby mode that may be remotely activated [8]. ...
... Low power CMOS instrumentation circuits have speeds that far exceed this low sample rate. Significant power may be saved by strategically turning off circuit components between sample periods [7]. Here, we demonstrate a power management strategy that sequentially switches the bias point of circuits. ...
Conditional neuromodulation in which neurostimulation is applied or modified based on feedback is a viable approach for enhanced bladder functional stimulation. Current methods for measuring bladder pressure rely exclusively on external catheters placed in the bladder lumen. This approach has limited utility in ambulatory use as required for chronic neuromodulation therapy. We have developed a wireless bladder pressure monitor to provide real-time, catheter-free measurements of bladder pressure to support conditional neuromodulation. The device is sized for submucosal cystoscopic implantation into the bladder. The implantable microsystem consists of an ultra-low-power application specific integrated circuit (ASIC), micro-electro-mechanical (MEMS) pressure sensor, RF antennas, and a miniature rechargeable battery. A strategic approach to power management miniaturizes the implant by reducing the battery capacity requirement. Here we describe two approaches to reduce the average microsystem current draw: switched-bias power control and adaptive rate transmission. Measurements on human cystometric tracings show that adaptive transmission rate can save an average of 96% power compared to full-rate transmission, while adding 1.6% RMS error. We have chronically implanted the wireless pressure monitor for up to 4 weeks in large animals. To the best of our knowledge these findings represent the first examples of catheter-free, realtime bladder pressure sensing from a pressure monitor chronically implanted within the bladder detrusor.
Control of urine leakage is of major importance to spinal cord injured (SCI) patients and the elderly, with untreated urinary incontinence leading to contact dermatitis and pressure ulcers due to prolonged exposure to excess moisture. In one study, 81% of all patients with pressure ulcers had urinary incontinence. In addition, pressure ulcers exposed to urine are more susceptible to infection since the urine alters the pH balance of the skin and reduces resistance to bacterial invasion. Both SCI patients and the elderly are highly susceptible to incontinence, which is classically divided into two major types: overactive bladder and stress urinary incontinence, both of which can lead to uncontrolled urine leakage.
Implantable medical devices intended for chronic application in deep bodily organs must balance small size with battery capacity. Wireless battery recharge of implanted sensors is a viable option to reduce implant size while removing the physical and regulatory hindrance of continuous RF powering. This paper presents wireless battery recharge circuitry developed for an implantable pressure sensor. The circuits include an RF/DC rectifier, voltage limiter, and constant-current battery charger with 150-mV end-of-charge hysteresis. An AM demodulator drawing zero DC current allows for transmission of commands on the recharge carrier. Reception of a time- and value-coded shutdown command places the implantable system into a 15 nanoampere standby mode. The system can be wirelessly activated from standby by reactivating the external wireless recharge carrier. Test results of the wireless system showed a standby current of 15-nA such that the implant standby time is limited by battery self-discharge. Wireless recharge tests confirmed that a constant recharge rate of 200 μA could be sustained at implant depths up to 20 cm, but with low power transfer efficiency <; 0.1% due to small implant coil size. Battery charge measurements confirmed that daily 4-hour recharge periods maintained the implant state of charge and this recharging could occur during periods of natural patient rest.
