A highly digital VCO-Based ADC architecture for current sensing applications

Praveen Prabha, Seong Joong Kim, Karthikeyan Reddy, Sachin Rao, Nathanael Griesert, Arun Rao, Greg Winter, Pavan Kumar Hanumolu

Research output: Contribution to journalArticlepeer-review


This paper presents a voltage-controlled oscillator (VCO) based current to digital converter for sensor readout applications. Second order noise shaping of the quantization error is achieved by using implicit capacitance of the sensor to realize a passive integrator and a VCO-based quantizer. The non-linearity in voltage to frequency conversion of the VCO is tackled by placing the VCO in a loop consisting of a simple digital IIR filter and a passive integrator. The IIR filter provides large gain within the signal bandwidth and suppresses VCO input swing. As a result, non-linearity of the VCO is not exercised, thus greatly improving the proposed architecture's immunity to VCO nonlinearity. The use of a digital filter instead of an analog loop filter eases the design and makes it scaling friendly. Designed for an ambient light sensor application, the proposed circuit achieves 900 pA accuracy over an input current range of 4 μA. Fabricated in a 0.18 μ m CMOS process, the readout circuit consumes a total of 77.8 μ A current, and occupies an active area of 0.36 mm2.

Original languageEnglish (US)
Article number7084688
Pages (from-to)1785-1795
Number of pages11
JournalIEEE Journal of Solid-State Circuits
Issue number8
StatePublished - Aug 1 2015


  • VCO based ADC
  • ambient light sensor
  • analog-to-digital conversion
  • current sensor
  • delta-sigma modulation
  • digital readout circuits
  • sensor applications
  • time based ADC

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


Dive into the research topics of 'A highly digital VCO-Based ADC architecture for current sensing applications'. Together they form a unique fingerprint.

Cite this