A 4-GHz Active Scatterer in 130-nm CMOS for Phase Sweep Amplify-and-Forward

Abstract

This article demonstrates the cooperative diversity improvement achieved using a 120-W active scatterer built in 130-nm CMOS technology. The low-power all-analog device acts as a repeater, or relay, for phase sweep amplify-and-forward cooperative transmission. The device relies on microwave reflection to amplify, dynamically phase modulate, and reradiate the incident signal. This reduces the duration of the fades experienced in the indoor radio channel and improves error correction code performance. Radio channel propagation measurements collected using the relay prototype clearly show the effect of the phase modulation on fading and system level simulations conducted using the propagation data show a fivefold increase in coverage area.

Enhancement of RF Tag Backscatter Efficiency With Low-Power Reflection Amplifiers

“…Notice that while the input power increases, the amplifier experiences a gain compression. This effect is anticipated and it has been reported in the literature [21].…”

“…This property leads to compact low-profile circuits, and consequently has been proposed in active antenna implementations for RFID applications, such as in [19] and [20] where 5.25-and 21-GHz tags utilizing reflection amplifiers are proposed. Furthermore, reflection amplifiers have been considered in active reflector circuits used as amplify and forward active antennas in wireless communication scenarios [21]. The negative resistance amplifier concept is attributed to Armstrong [22], [23].…”

“…Consequently, a challenge in such circuits consists in controlling the stability of the circuit [15], [19], [21], as well as its bandwidth [26].…”

“…The amplifiers used in [19] and [20] that are used for tagging applications, similar to the tagging/sensing applications this work's system is targeted, require significantly higher bias voltage of over 2 V for comparable gain values and their power dissipation is on the order of milliwatts. The amplifier in [21] is used for analog relaying and is implemented in 130-nm low-power CMOS technology and achieves an ultra-low-power consumption of 0.120 mW. Although this work's amplifier is built using discrete components, its consumption of 0.325 mW is on the same order of magnitude with that of the low-power CMOS circuit.…”

“…Considering a reader that transmits power towards a tag placed at a distance of meters, the received backscattered power due to round-trip path loss is (20) Consider also a tag with increased backscattered power by 8 dB that is placed m away from the reader, and the reader receives the same backscattered power level (21) It can then be calculated that the tag-to-reader range relation between tag 1 and tag 2 is (22) i.e., a range increase of up to 26% can be achieved.…”