Analog-to-digital converter circuitry, an integrated circuit device, a photoplethysmogram detector, a wearable device and a method for analog-to-digital conversion

An analog-to-digital converter, ADC, circuitry, comprising:

• an input for receiving an analog input signal to be converted to a digital representation, and a reference input signal;
• an integrator connected to a capacitor, wherein the integrator is configured to switch between integrating the analog input signal for ramping an integrator output and allow a charge to build up on the capacitor and integrating the reference input signal for returning integrator output towards a threshold;
• a comparator for comparing integrator output to the threshold;
• and
• a timer for determining a time duration during which the reference input signal is integrated for changing the integrator output to reach the threshold, wherein the time duration provides a digital representation of an analog input signal value;
• wherein the ADC circuitry further comprises a feedforward noise shaping loop comprising at least one noise shaping capacitor configured to store a quantization error signal remaining on the integrator output based on digitizing a first sample of the analog input signal, wherein the comparator is configured to receive a feedforward noise shaping signal from the feedforward noise shaping loop based on the quantization error signal stored by the at least one noise shaping capacitor for changing the threshold of the comparator for digitizing a later sample of the analog input signal following the first sample.