Abstract
This study presents a low-power Zigbee receiver with a current-reusing structure and function-reused mixing techniques. To reduce the overall power consumption, a low noise amplifier (LNA) and a power amplifier (PA) share the biasing current with a voltage-controlled oscillator (VCO) in the receiving (RX) mode and transmitting (TX) mode, respectively. The function-reused mixer reuses the radio frequency trans-conductance (RF gm) stage to amplify the down-converted intermediate frequency (IF) signal, obtaining a free IF gain without extra power consumption. A peak detector circuit detects the receiving signal strength and auto-adjusts the biasing current to save power when a strong signal strength is detected. Meanwhile, the peak detector helps to provide a coarse gain control as part of the auto-gain-control function. As part of the IF gain range is shared by the multiple-feedback (MFB) low-pass filter, the number of programmable-gain IF amplifier stages can be reduced, which also means a decrease in power consumption. A prototype of this wireless sensor network (WSN) receiver was designed and fabricated using the TSMC 130 nm CMOS process under a supply voltage of 1 V. The entire receiver realizes a noise figure (NF) of 3.5 dB and a receiving sensitivity of −90 dBm for the 0.25 Mbps offset quadrature phase shift keying (O-QPSK) signal with a power consumption of 2.9 mW.
Highlights
In today’s handset wireless communication devices such as cell phones, handset GPS terminals, and wireless body sensors, achieving a low power consumption is the primary target to prolong the recharging cycle
The recursive mixer reuses the RF gm stage to amplify both the RF signal and the down-converted intermediate frequency (IF) signal
For a traditional recursive mixer, the RF gm stage is used to amplify the down-converted IF signal [5,6]
Summary
In today’s handset wireless communication devices such as cell phones, handset GPS terminals, and wireless body sensors, achieving a low power consumption is the primary target to prolong the recharging cycle. In a RF receiver, the low noise amplifier (LNA), power amplifier (PA), mixer, and voltage controlled oscillator (VCO) work in the RF frequency range and dominate the total power consumption. The receiver front end is formed by the cascading of a current-reusing LNA and the mixer. Since the LNA provides a preceding voltage gain, both a high conversion gain and a low noise figure are achieved. When the input signal power is below −60 dBm, the biasing current of the mixer is automatically turned up by the analogue gain-control loop, and provides a high conversion gain to guarantee a sufficient signal-noise-ratio (SNR). Performance indexes, such as NF, power consumption, gain and Input 3rd order intercept point (IIP3), are designed, balanced, and optimized. Equation (2) reveals that the linearity of the back-end stages plays a more important role in realizing a high total IIP3
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