A time-to-digital converter based AFC for wideband frequency synthesizer

Deping Huang, Wei Li, Jin Zhou, Ning Li, Junyan Ren, Jinghong Chen

Research output: Contribution to journalArticlepeer-review


The automatic frequency calibration (AFC) technique is routinely used in wideband frequency synthesizers that contain multiple voltage-controlled oscillator (VCO) tuning curves. In this paper, a counter-based AFC that uses a time-to-digital converter (TDC) in the counting process is developed. The TDC is able to capture the fractional VCO cycle information within the counting window. This significantly improves the frequency detection accuracy over the existing counter-based AFC techniques. In addition, a quantitative model is developed to determine the minimally required error-free AFC calibration time for a given VCO tuning curve characteristic. An AFC circuit using the proposed TDC-based counter is designed in a 0.13-μm CMOS technology. Simulation results show that the proposed AFC significantly improves the frequency detection accuracy and consequently for a given frequency detection resolution reduces the AFC calibration time. The simulated error-free AFC time is <2.5 μs with a frequency resolution of 0.04 %.

Original languageEnglish (US)
Pages (from-to)207-217
Number of pages11
JournalAnalog Integrated Circuits and Signal Processing
Issue number2
StatePublished - May 2014
Externally publishedYes


  • Automatic frequency calibration
  • Frequency synthesizer
  • Phase-locked loop
  • Voltage controlled oscillator

ASJC Scopus subject areas

  • Signal Processing
  • Hardware and Architecture
  • Surfaces, Coatings and Films

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