Fabio Gozzini

Transimpedance Amplifier for High Sensitivity Current Measurements on Nanodevices

The paper presents a very high sensitivity transimpedance amplifier in standard CMOS 0.35 mum technology suited for sensing current signals from molecular and nanodevices systems. The circuit, based on an integrator followed by a differentiator configuration, features i) a low-noise time-continuous feedback loop to cope with possible standing currents from the device under test as high as few tens of nA without limiting the signal dynamic range; ii) active current-reducers to implement very high value equivalent resistances of hundreds of GOmega with high linearity irrespective to the current direction and characterized by a shot noise current level (2qI) which is, for low standing current, few orders of magnitude smaller than a physical resistor of equal value and iii) nested-Miller compensation networks to ensure strong stability over a bandwidth of few MHz. Thanks to the ability to draw large standing currents, the circuit is suitable for a use in biological systems where physiological medium is co-present. The measured input equivalent noise of 4 fA/radic(Hz) at about 100 kHz, recorded when the input dc current is lower than 10 pA, allows the chip to be used, among others, in impedance spectroscopy measurements at the nanoscale with a capability of detecting capacitance variations in sub-attofarad range to cope with the challenges of single-chip instrumentation.

A Current-Sensitive Front-End Amplifier for Nano-Biosensors with a 2MHz BW

Active resistors up to 300GOmega operating down to the fA range are implemented in the feedback path of an integrator-differentiator transimpedance amplifier for high-sensitivity current measurements. The system has 4fA/radicHz noise up to 100kHz, a 2MHz bandwidth, and ensures unlimited measuring time even with nA DC input currents

An instrument-on-chip for impedance measurements on nanobiosensors with attoFarad resoution

Impedance measurements play a fundamental role in biotechnology, serving both as an investigation tool and as a direct detection technique. Tracking impedance over time is extensively used for spatial monitoring, imaging, counting, sizing (Coulter counter) and sorting cells (flow cytometry) both in macro and microfluidic systems [1]. Other than cellular biology, impedance measurements are largely used also in molecular biology to operate affinity molecular biosensors [2], where impedance measurements are used to detect the binding of a target molecule to highly specific biological macromolecules such as antibodies, receptors, enzymes and DNA strands. Downscaling these systems to nanoscale dimensions would offer tremendous advantages as compared to the currently existing macro and microscale counterparts on three essential aspects, namely sensitivity (detection of single molecule binding events), response time (more efficient diffusion of the analyte) and amount of sample analyte [3]. Monitoring single molecules implies very small absolute impedance variations, on the order of a few attoFarads for the capacitive term, which should be detected by applying only a few tens of millivolts to avoid stressing the macromolecule with high electrical fields.

A 0.18μm CMOS 91%-efficiency 0.1-to-2A scalable buck-boost DC-DC converter for LED drivers

Several emerging portable applications require high-efficiency LED drivers [1-4]. An LED driver is basically a current source that forces the current required for achieving the desired light emission into the LED. In order to increase the LED driver efficiency, besides controlling the LED current, it is necessary to regulate the voltage applied to the LED itself, to minimize the voltage drop across the driver current source and, hence, the power consumption. Depending on the kind of LED and on the current forced through the LED itself (0.1 to 2A in this design) and, hence, on the desired light emission, the voltage required to drive the LED, while maintaining the voltage headroom across the driver current source to the minimum, varies over a wide range (0 to 5V). Starting from a standard voltage supply in the range 2.7 to 5.5V, a buck-boost DC-DC converter is then required (Fig. 16.4.1). The buck-boost DC-DC converter includes the LED in the control feedback loop and has to provide fast turn-on and load transients (on the order of 20μs), in order to allow pulsed operation of the LED itself.

Transimpedance amplifier for very high sensitivity current detection over 5MHz bandwidth

The paper presents a transimpedance amplifier made on standard 0.35 mum CMOS technology specifically conceived to measure the impedance of low-conductivity nano-bio devices. The circuit combines a bandwidth of 5 MHz with an extremely low noise of 3 fA/sqrt (Hz) by using an integrator-differentiator scheme. An innovative feedback network continuously discharges the integrator capacitance to ensure an unlimited measuring time irrespective of the do input current up to 20 nA. An highly linear 300 GOmega active resistance, used in the feedback network to extend the lower limit of the bandwidth down to 100 Hz, will be also described.

Very high sensitivity CMOS circuit to track fast biological current signals

The paper presents a novel transimpedance amplifier to sense very small and fast biological signals even in the presence of a dc leakage current as high as few tens of nanoamperes. The circuit, integrated on standard 0.35 mum CMOS technology, has a core based on the series of an integrator and a differentiator stage but features an additional time continuous feedback loop to discharge the standing current from the device under test, thus ensuring an unlimited measuring time opportunity with no need of reset pulses. This amplifier is ideal in a wide range of applications in miniaturized single chip systems such as implantable electronics, single molecules characterization or sensor interfaces, where very high sensitivity is requested together with minimum amount of biological matter and of analyte.

Transimpedance Amplifiers for Extremely High Sensitivity Impedance Measurements on Nanodevices

The paper highlights the critical aspects in the design of high performance transimpedance amplifiers to be used for the electrical characterisation of nano-biodevices. Current sensitivity, bandwidth, dynamic range and leakage current discharge are discussed to cope the tight needs in impedance spectroscopy measurements at the nanoscale. An implementation in a standard 0.35 UPmum CMOS technology using dual power supply of ± 1.5 V is described in detail: thanks to an active resistor of equivalent value up to 300 GΩ and minimum noise, a transimpedance amplifier operating from few Hz is obtained, featuring an operative dynamic range for ac current signals independent of the amount of the leakage current and allowing an unlimited measuring time, ideal for attoFarad capacitance measurements of biological samples in their physiological medium.

Instrumentation with attoFarad resolution for electrochemical impedance measurements on molecular biosensors

Sub-attoFarad capacitance resolution is experimentally reached, demonstrating the suitability of the proposed instrumentation for the development of impedimetric molecular biosensors. The modular design of the system is illustrated along with novel analog solutions (providing high sensitivity over a DC-1MHz bandwidth), digital lock-in elaboration techniques and their impact on the final instrument resolution.