Low offset automatic frequency tuning circuits for continuous-time filter

Abstract

The present invention relates to a tuning circuit, more specifically to a tuning circuit for continuous-time filter capable of making exact the Gm value to minimize the variation of the cutoff frequency due to the variation of process in the Gm-C type of continuous-time filter. According to the invention, a frequency tuning circuit is provided which comprises integrating means for generating a signal discharging from a first reference voltage to a first predetermined value and a signal charging from a second reference voltage to a second predetermined value; offset sampling means for sampling the offset voltages of the Gm cells by receiving a current multiplied by the offset voltages from the Gm cells included in the integrating means and providing a feedback path between the output nodes and the input nodes of the included Gm cells; comparative signal generating means for generating a comparative signal by generating a reference signal by dividing a clock inputted from the external, receiving the signal discharging from the first reference voltage to the first predetermined value and the signal charging from the second reference voltage to the second predetermined value from the integrating means, and comparing the actual intersection and the target intersection of these signals; and control means for generating a control signal to regulate the Gm values of the integrating means and the offset sampling means by receiving the reference signal and the comparative signal from the comparative signal generating means and detecting the phase differences therebetween.