The performance of differential up-conversion passive mixer operating in the 3-5 GHz band for UWB transmitter driven by 25% duty-cycle clocks is studied and analyzed. A reasonably accurate LTI equivalent circuit accounting for harmonics is derived. We have demonstrated that the conversion gain, input and output impedances of the proposed LTI equivalent circuit matches those of the LTV up-conversion passive mixer. The LTI model can be used to define the reachable design space. The mixer input and output impedance can be tuned by varying resistor at the mixer output allowing for impedance match to connected circuits. We have shown how each design parameters impacts critical performance of the up-conversion passive mixer. Simulations of the proposed up-conversion passive mixer show À3.68 dB of conversion gain, 15.9 dBm of OIP3, 116.7dBm of OIP2 and a NF as low as 5.2 dB while consuming 1.5 pW. Furthermore linearity and ports isolation performances due to voltage threshold mismatch variation of ±60 mV shows an OIP3 greater than 15.85dBm and an LO_RF isolation smaller than À51.9 dB.
This paper presents the design of a Chirp Spread Spectrum (CSS), ultra-wideband (UWB), pulse generator (PG) and device mismatch impact on its performance. The proposed CSS-PG is built using a differential ring oscillator (RO) controlled by a ramp generator, allowing varying linearly the pulse frequency with time over the CSS pulse duration. Device mismatches and random variations during integrated circuit manufacturing are the most critical imperfections in high precision differential UWB voltage controlled RO circuit. These mismatches lead to behavioral variations of the PG. The proposed CSS-UWB-PG is designed and analyzed using CMOS 0.18[Formula: see text][Formula: see text]m technology. The CSS-PG presents an output swing of 266[Formula: see text]mV Vpp for 20[Formula: see text]nsec and consumes 1.72[Formula: see text]mW for a PRF of 10[Formula: see text]MHz. The simulated PSD covers the UWB low band from 3[Formula: see text]GHz to 5[Formula: see text]GHz and complies with the FCC regulations. For [Formula: see text] mismatch, the simulation results show a maximum relative accuracy on oscillation frequency and phase noise of 3.43% and 6.9%, respectively. Monte Carlo and process simulation are performed to study the impact of the random parameter variation on this CSS-PG. Theses simulations show the robustness of the proposed design as the PG PSD is still inside the FCC-UWB mask and its bandwidth is greater than 500[Formula: see text]MHz.
A low-complexity dual-band chirp FSK, direct conversion receiver is described in this paper. The receiver is dedicated to be used in the transceiver unit of a medical implantable wireless sensor. The system uses the RF band between 402 and 405 MHz. Two sub-bands frequencies employing chirped pulses are assigned for both binary information. The novelty of this work is the use of a Binary FSK LFM modulator, a direct conversion receiver and a simple and low power non-coherent BFSK envelope detection demodulator. Receiver performances are evaluated for all the input power dynamic range. Receiver front-end parameters are optimized using harmonic balance simulation. In order to improve receiver sensitivity, a low pass filter with controllable bandwidth between 40 and 300 KHz is used to avoid in-band interference. The receiver is able to achieve a noise figure of 5.5 dB, a receiver sensitivity of-93 dBm and a maximum data rate of 100Kbps. The simulated IIP3 and P-1dB are 12.6 dBm and 22.1 dBm respectively. A simple non coherent binary dual band FSK demodulator was used which is based on an envelope detector, integrate & dump, a sampling & hold and a liming circuit. The receiver was co-simulated with the dual band non coherent demodulator. The proposed receiver has a sensitivity of-93 dBm and a BER less than 10-3 .
Today it is important to manufacture high quality integrated circuits which are insensitive to device mismatches. This paper presents an analysis of MOSFET transistors mismatches effect on the performance of UWB receiver front-end which constitute the most important part of Wireless Body Area Network sensor node. The receiver is based on Balun LNA with 25% fully differential double-balanced passive mixer. A PMOS and NMOS transistors mismatch models were proposed to determine LNA output offset voltage and mixer offset current respectively. The analysis result suggests that, to minimize NMOS current mismatch, and thus reducing second-order inter modulation distortion, the overdrive voltage must be maximized. A Monte Carlo and harmonic balance simulations were performed using 0.18µm CMOS process to evaluate the impact of mismatch as well as Vth mismatch on the receiver gain and IIP2. Simulation results show that IIP2 of the receiver is less sensitive to mixer NMOS mismatch but receiver gain is more sensitive. The receiver IIP2 confidence interval in case of NMOS mismatch is [24.674, 24.77]dBm and in case of NMOS Vth mismatch is [24.659, 24.857]dBm. This show the robustness of the proposed UWB receiver front end. Therefore the proposed circuit meets the requirement of UWB system perfectly which make it suitable for WBAN applications.
This paper presents analysis of a 25% duty-cycle fully-differential double-balanced passive mixer dedicated to medical implantable devices. The proposed passive mixer is part of a medical implant communication service (MICS) receiver front-end operating at 402–405[Formula: see text]MHz. By performing time-domain analysis, two LTI models have been developed to study the fully-differential double-balanced passive mixer: A simplified model and a complete model taking into account harmonic components. Both models account for the AC coupling capacitors at the mixer input and account for baseband voltage variation over one LO period. In this study it has been shown the ability of mixer input impedance matching by varying baseband resistor at the mixer output. The frequency of match can be controlled by varying the AC coupling capacitors and baseband capacitors. The performance of the proposed models was compared with that of the mixer and the results were very close. In particular, the results of simulations of the input impedance as a function of the baseband resistance and as a function of the IF frequency show the validity of the proposed models. The main parameters of the passive mixer such as input impedance, gain and noise figure (NF) were optimized taking into account the constraints of our application. The proposed mixer is designed to operate at LO frequency of 403.2[Formula: see text]MHz. Transistors size is optimized to meet the receiver specifications. The mixer realizes a conversion gain of 0[Formula: see text]dB and an NF of 4.8[Formula: see text]dB. Linearity simulations show 25.2[Formula: see text]dBm for IIP3 and 9.66[Formula: see text]dBm for [Formula: see text]dB. The mixer consumes 1.44[Formula: see text]pW without LO circuit.
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