Digital filter for phase-locked loop integrated circuits

摘要

A digital filter for a frequency synthesizer (e.g., PLL, UFT) may include an analog-to-digital (ADC) converter, which is responsive to a control voltage at an input thereof, and a digital-to-analog (DAC) converter, which has an input responsive to a signal generated at an output of the ADC. An impedance element is provided between the DAC and ADC. The impedance element has real and reactive components, a first current carrying terminal electrically coupled to an output of the DAC and a second current carrying terminal electrically coupled to the input of the ADC. The impedance element can include a resistor and a capacitor, which are electrically connected in parallel. A gain device, such as a programmable multiplier, may also be provided, which has an input responsive to the signal generated at the output of the ADC and an output electrically coupled to the input of the DAC.

主权项

1. A phase-locked loop integrated circuit, comprising:
an analog-to-digital converter (ADC) responsive to a control voltage at an input thereof; a digital-to-analog converter (DAC) having an input responsive to an ADC output signal generated at an output of said ADC, said DAC input directly receiving a digital signal that retains all material digital information contained in the ADC output signal; and an impedance element having real and reactive components, a first current carrying terminal electrically coupled to an output of said DAC and a second current carrying terminal electrically shorted to the input of said ADC, said first current carrying terminal directly receiving an analog signal that retains all material analog information contained in a DAC output signal generated at the output of said DAC.