CMOS 8-channel frequency division multiplexer for 9.4 T magnetic resonance imaging

We present a CMOS 8-channel frequency division multiplexer (FDM) to interface a phased array of micro coils for 9.4 T (400 MHz Larmor precession frequency ω₀) for magnetic resonance imaging (MRI). The integrated multiplexer contributes towards a solution to achieve phased arrays with a massive number of coils without unnecessarily increasing system complexity, the size of hardware, and cost. The multiplexer is designed using commercially available 0.35 μm CMOS technology and consists of five major components: a low-noise amplifier (LNA), a frequency mixer, a voltage-controlled oscillator (VCO), a bandpass filter (BPF), and an adding operational amplifier. The maximum gain of a single channel is 79 dB, and the input referred noise is 1.4 nV/√Hz. The die area of the multiplexer is approximately 8 mm², and requires 300 mA from a 3.3 V source.