A Sub-mA FH Frequency Synthesizer Technique

Abstract

A novel frequency-hopping spread-spectrum transmitter architecture is presented that provides robust communications in the 915 MHz ISM band while dissipating very low power. The frequency-hopping front-end consists of a VCO, dividers and output stage. A base-band predistortion algorithm allows hopping with minimum hardware complexity. The TX front-end has been fabricated in Silicon-on-Anything (SOA) bipolar technology and a BFSK modulated wireless link using a dedicated receiver has been realized. A 1kbps, 1khop/s link with a BER smaller than 1.1 % has been achieved at -25 dBm output power while having 64 orthogonal channels. The synthesizer architecture (VCO+divider+base-band) dissipates only 870µA.

A 1 mA Ultra-Low-Power FHSS TX Front-End Utilizing Direct Modulation With Digital Pre-Distortion

“…This spectrum has been measured while using the front-end disclosed in this paper. However, it should be noticed that when calibrated to the same output power, the described front-end and the one disclosed by the authors in their previous works [2], [3], [9] give the same output spectrum. Only the absolute position of the frequency peaks will vary due to the process spread on the varactor C-V curves (DAC and board are kept the same).…”

“…Therefore, from the previous analysis it is possible to conclude that a good strategy toward the reduction in the average transmitter power consumption consists of reducing the data rate and decreasing the synchronization time for a given node duty-cycle. 3 1 The 2-FSK noise bandwidth can be approximated by the Carson rule as B = 2(1f + f ) where f = (2=T ) with T the symbol period. 2 For a 2-FSK modulated signal it equals four times the data rate.…”

“…2 For a 2-FSK modulated signal it equals four times the data rate. 3 In this analysis, the duty-cycle is fixed. This is the reason why the average power consumption does not increase at very low data rate.…”

“…Nevertheless, this architecture suffers from an important drawback: the disturbance coming from the PA output and being injected in the local oscillator (LO). This drawback can be alleviated by shifting the output spectrum far from the LO frequency [3] or by shielding the VCO tank from the antenna by using a current buffer. In this way, the front-end, in a single block, combines both the VCO required for the up-conversion and the PA required to transmit the information through the channel.…”

“…An implementation using this topology has been described in [3] and [9]. It consists of three different RF blocks: LC oscillator, frequency divider, and PA, and achieves good performances.…”