SAB based loop filter with cross-coupled structure and ADC including the same

An analog-to-digital converter (ADC) employing delta-sigma modulation, the ADC comprising:

• a loop filter configured to integrate a difference signal between an input signal and a feedback signal;
• a quantizer configured to quantize an output of the loop filter to output a digital signal;
• and
• a digital-to-analog converter (DAC) configured to convert the digital signal into an analog signal and provide the analog signal as the feedback signal,
• wherein the difference signal includes an in-phase (I) input signal and a quadrature (Q) input signal, and the loop filter performs single-amplifier biquad (SAB) multi-order integration on each of the I and Q input signals and feeds back each integration result using a respective cross-coupled path,
• wherein the loop filter comprises:
• a first SAB integrator configured to apply an integration operation to the I input signal;
• a second SAB integrator configured to apply an integration operation to the Q input signal;
• a first cross-coupled path configured to provide an output of the first SAB integrator to an input terminal of the second SAB integrator with a first gain;
• and
• a second cross-coupled path configured to provide an output of the second SAB integrator to an input terminal of the first SAB integrator with a negative of the first gain,
• wherein each of the first SAB integrator and the second SAB integrator comprises one operational amplifier, and
• wherein an output voltage of each one operational amplifier of the first SAB integrator and the second SAB integrator is configured to be fed back to an input of the each one operational amplifier of the first SAB integrator and the second SAB integrator via an inverting circuit, a ‘−1’ gain resistor, and a ‘−1’ gain capacitor, the inverting circuit representing a ‘−1’ operator.

A loop filter, comprising:

• a first integrator configured to apply an integration operation to an in-phase (I) input signal;
• a second integrator configured to apply an integration operation to a quadrature (Q) input signal;
• and
• a cross-coupled path configured to cross-transfer an output voltage of the first integrator to an input side of the second integrator, and an output voltage of the second integrator to an input side of the first integrator,
• wherein at least one of the first integrator or the second integrator performs the respective integration operation using a single-amplifier biquad (SAB) integrator configuration,
• wherein the SAB integrator configuration includes an SAB integrator comprises one operational amplifier, and
• wherein an output voltage of the one operational amplifier is configured to be fed back to an input of the one operational amplifier via an inverting circuit, a ‘−1’ gain resistor, and a ‘−1’ gain capacitor, the inverting circuit representing a ‘−1’ operator.