An ultra-low power ISM-band integer-N frequency synthesizer dedicated to implantable medical microsystems

Abstract

In this article, the architectural choices and design of a fully integrated integer-N frequency synthesizer operating in the 902-928 MHz Industrial, Scientific and Medical (ISM) band is presented. This frequency synthesizer, optimized for ultra-low power operation, is being integrated in the transceiver of an implantable wireless sensing microsystem (IWSM), which is dedicated to in vivo monitoring of biological parameters such as temperature, pressure, pH, oxygen, and nitric oxide concentrations. This phase-locked loop-based synthesizer includes a 1.830 GHz LC voltage-controlled oscillator (VCO) using a 10 nH on chip inductor. Varactors are implemented using P+ in N-well diodes for their linearity and high quality factor. The transistors of the VCO are operated in moderate inversion, and their bias point was chosen using the g m /I d design methodology. The output of the VCO, operating at twice the ISM frequency band, is divided by 2 to generate differential, quadrature versions of the carrier. Power minimization of the programmable divider was achieved by designing the latches and flip-flops using appropriate circuit techniques such as True Single Phase Clocking (TSPC) and first-type Dynamic Single Transistor Clocking (DSTC1) depending on their operating frequency. The power consumption of the proposed synthesizer is 580 lW under 1 V; almost an order of magnitude lower compared to that of recent synthesizer designs having a similar architecture.

A new FSK-based transmitter dedicated for low-power wireless medical transceivers

“…The simulation is done in Cadence environment using TSMC90nm technology with supply voltage of 1.2 V. the voltage supply used for the local oscillator is 1 V [2]. Table 1 shows the simulation results of this work comparing with other works with similar specifications such as operating frequency.…”

“…An ultra low-power integer-N frequency synthesizer in [2] generates the In-and Quadrature-Phase (I/Q) signals to use in a Direct-Up Conversion architecture ( Fig. 2) with the proposed modulation scheme which mainly includes a Phase-Shifter, Modulator, Mixer and a Power Amplifier (PA).…”

“…Since the amplitude of the FSK signal is constant, a nonlinear PA with high efficiency can be used to implement the transmitter while saving the power budget. Also, that the synthesizer circuit, described in [2], generates stable In-and Quadrature-Phase (I/Q) versions of the Local Oscillator signals and uses a 1 V supply voltage.…”

“…Also, image-reject architectures need high I/Q matching and even a two-step-up conversion still suffers from image problem. In practice, generating stable I/Q signals with reliable frequency and transient characteristics increases the quality of the signal in transceivers [2]. Low cost, high integrability, simplicity and having no image problem make the Zero-IF/Direct-Up Conversion architectures suitable for implantable transceivers.…”

A low-voltage low-power injection-locked oscillator for wearable health monitoring systems

“…The reported transmitter (operating at 1.9 GHz) shows 32% efficiency at 0 dBm output power from a 280 mV supply. Tanguay and Sawan [6] have reported the simulation results of an integer-N frequency synthesizer for implantable medical microsystems using 90-nm CMOS process. The synthesizer can work with a supply voltage of 1 V with an operating frequency of 915 MHz and consumes 578 lW of power.…”