FBH Research: 23.02.2012

A 24-GHz-CMOS-VCO for Localization purposes

Oscillator CMOS Technology
Fig 1. Two versions of a voltage controlled oscillator (VCO) for 24 GHz in 130 nm CMOS technology.
Phase Noise Characteristics
Fig. 2. Single sideband phase noise of both VCO versions vs. carrier offset frequency.

Just imagine two robot welders, together assembling a car body with high speed and high force. If they crash, the damage will be expensive: Not only the robots will be damaged, but also the assembly line will have to stop. In near future, such pitfalls can be avoided using two tiny localization blocks placed on each robot’s arm. These localization blocks are able to measure the distance to each other and to provide early warning of collisions.

The localization block is based on radar principle at 24 GHz and its core is a voltage controlled oscillator (VCO) generating the radar signal. For high localization accuracy in the range of a fraction of an inch it is necessary to have a radar signal with low phase noise. This is due to the fact that phase noise directly determines the localization accuracy. In the framework of the BMBF project LoWiLo (Low-power Wireless Sensor Network with Localization), such a 24 GHz low phase-noise VCO was developed at FBH [1]. Based on an advanced 130 nm CMOS technology, some versions of cross-coupled VCO were designed and characterized.

The two versions differ in the choice of the frequency-determining spiral inductor with respect to its quality factor and in the way the varactor is coupled, see Fig. 1. Fig. 2 presents the phase noise spectrum of both versions of the VCO. Clearly, version B exhibits a phase noise lower than that of version A by 10 dB at 100 kHz offset, which translates into enhanced localization accuracy.

Publication:

[1] Hossain, M.; Kravets, A.; Pursche, U.; Meliani, C.; Heinrich, W.: "A Low Voltage 24 GHz VCO in 130nm CMOS For Localisation Purposes in Sensor Networks," paper to be presented at German Microwave Conference 2012 in Ilmenau (Session 12, 13 March 2012).