This thesis describes the design and implementation of integrated high-side current sensors for IoT applications. As explained in chapter 1, the main challenges are the need to achieve low power, low cost and low area while maintaining a reasonably low gain error. To meet them, the focus of this thesis is on (1) the design of precision HV interface circuitry that does not need a HV supply, and (2) the design of energy-efficient temperature compensation schemes that enable the integration of shunt resistors with CMOS circuitry. Several new techniques at both system-level and circuit-level have been proposed and their effectiveness is verified in two prototypes. An integrated shunt-based current sensor consists of an interface circuit, a shunt resistor and a temperature compensation scheme. Chapter 2 gives an overview of these three elements. It first describes two sensing configurations: low-side sensing and high-side sensing, followed by a discussion of their pros and cons. High-side sensing is favored because of its ability to avoid the ground disturbance and detect the high load current caused by accidental shorts. However, it makes the design of the HV interface circuitry more challenging, as this must accurately and safely extract weak differential signals in the presence of large CM voltages. Several existing solutions are reviewed. However, these either consume too much power or occupy large silicon area. This observation leads to the first challenge addressed by this thesis: the design of power-efficient and compact HV circuitry for high-side current sensing. In the two prototypes described in this thesis, low-cost shunt resistors based on the metal layers of a CMOS process, or the lead-frame of a standard plastic package were used. However, both of them suffer from a large temperature coefficient of resistance (TCR) (>0.3%/°C), and so a temperature compensation scheme is necessary to achieve reasonable low inaccuracy. Two types (analog and digital) of temperature compensation schemes are reviewed. Analog ones achieve poor (>1%) inaccuracy while digital ones need a dedicated temperature sensor and a rather complex calibration process. This leads to the second challenge that this thesis addresses: the design of temperature compensation schemes that are low power and easy to use, while still achieving reasonable low inaccuracy. @en

This paper presents a fully integrated ±4A current sensor that supports a 25V input common-mode voltage range (CMVR) while operating from a single 1.5V supply. It consists of an on-chip metal shunt, a beyond-the-rails ADC [1] and a temperature-dependent voltage reference. The beyond-the-rails ADC facilitates high-side current sensing without the need for external resistive dividers or level shifters, thus reducing power consumption and system complexity. To compensate for the shunt's temperature dependence, the ADC employs a proportional-to-absolute-temperature (PTAT) reference voltage. Compared to digital temperature compensation schemes [2,3], this analog scheme eliminates the need for a temperature sensor, a band-gap voltage reference and calibration logic. As a result, the current sensor draws only 10.9μA and is 10x more energy efficient than [2]. Over a ±4A range, and after a one-point trim, the sensor exhibits a 0.9% (max) gain error from -40°C to 85°C and a 0.05% gain error at room temperature. The former is comparable with that of other fully-integrated current sensors [2-4], while the latter represents the state-of-the-art.

@en

This letter presents the most accurate shunt-based high-side current sensor ever reported. It achieves a 25 V input common-mode range from a single 1.8-V supply by using a beyond-the-rails ADC. A hybrid analog/digital temperature compensation scheme is proposed to simplify the circuit implementation while maintaining the state-of-the-art accuracy. Over a ±12-A current range, the sensor exhibits 0.35% gain error from -40 °C to 85 °C with 3× better power efficiency.@en

This paper presents a fully integrated shunt-based current sensor that supports a 25-V input common-mode range while operating from a single 1.5-V supply. It uses a highvoltage beyond-the-rails ADC to directly digitize the voltage across an on-chip shunt resistor. To compensate for the shunt’s large temperature coefficient of resistance (∼0.335%/°C), the
ADC employs a proportional-to-absolute-temperature voltage reference. This analog compensation scheme obviates the need for the explicit temperature sensor and calibration logic required by digital compensation schemes. The sensor achieves 1.5-μVrms noise over a 2-ms conversion time while drawing only 10.9 μA from a 1.5-V supply. Over a ±4-A range, and after a one-point trim, the sensor exhibits a 0.9% (maximum) gain error from −40 °C to 85 °C and a 0.05% gain error at room temperature.@en

This paper presents an NPN-based temperature sensor intended for the temperature compensation of the metal shunt resistor of an integrated current sensing system. The sensor was implemented in a 0.18 HV BCD CMOS technology and occupies 0.16mm² After a one-point trim, its inaccuracy is less than ±0.4°C over the industrial temperature range (-40°C to 85°C). It also achieves 14.8niK resolution in a 7ms conversion time while consuming 12μm. This results in a resolution FOM of 18.4pJ·K² the lowest ever reported for an NPN-based sensor.

@en

This paper presents a 15-bit ΔΣ ADC with 10kHz-BW which can handle 30V CM voltages with high AC CMRR (in excess of 115dB at 10kHz) while operating from a 1.8 V supply. An HV capacitively-coupled chopper at its input enables the accurate sampling of input signals beyond the supply rails. Chopping is used to mitigate the ADC's offset and to enhance its CMRR, especially at high frequencies.@en