Integrated circuit design for annular capacitive micromachined ultrasonic transducer

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Electrical and Electronics Engineering, Turkey

Approval Date: 2015


Supervisor: BARIŞ BAYRAM


The conventional ultrasound systems consist of many separated parts, and the bulky cables for connections result in a problem to be resolved. The systems with integrated interface electronics preferable since the removal of bulky cables resolves the signal degradation problems. In this thesis, a flexible and high drive capability digitally controlled beamformer is designed. The beamformer is designed to be integrated with annular capacitive micromachined ultrasonic transducer (CMUT) arrays. Although the beamformer designed in this thesis is intended to be used with therapeutic ultrasound systems, it may be used as transmitter block of an ultrasound imaging system. The aim of the beamformer is to focus the acoustic waves generated by the CMUT elements into a focal point to increase the energy at that point. The application of increasing this energy by focusing the acoustic waves is called high intensity focused ultrasound (HIFU). The system is designed in high voltage 0.18 μm CMOS process which offers 45 V at the output. The system consists of power conservative 2x1 demultiplexers (8.8 μW), oneshot circuits that generate single pulses with adjustable pulse widths (30 μW), digitally controlled oscillators that generates pulse trains at variable frequencies (246.3 μW), frequency down converters (203.5 μW), 8x1 and 4x1 multiplexers (5.64 μW and 94 nW), medium voltage pulsers (313 μW), and high voltage pulsers (148.5 mW). The oneshot circuit generates output pulses with 2.5 ns resolution. The duration of the output pulses can be any value that is multiple of 2.5 ns. The digitally controlled oscillator generates pulse trains with frequencies in the range of 20 to 312 MHz. The high voltage pulser circuit can drive loads up to 10 pF. The figure of merit which is defined as (delay/(node length x voltage)) characterizes the performance of pulsers and it is 0.49 for the high voltage pulser. In this work, 4 different beamformers are designed for 1x4, 4x1 and 4x4 annular CMUT arrays, and a test cell composed of all designed blocks is also laid out for economical testing purpose. The total chip area required for the test cell, 1x4, 4x1 and 4x4 cells are 6.68 mm2, 1.94 mm2, 4.07 mm2 and 30.73 mm2 respectively.