The present disclosure relates to integrators, and specifically to integrators suitable for continuous-time ΔΣ modulators.
Oversampling A/D converters are widely used, for example, for front-ends of communication devices and conversion of audio signals, and are now essential circuit techniques for communication systems and image/audio signal processing circuits. An example of such oversampling A/D converters is a continuous-time delta-sigma A/D converter (CTDS-ADC) including a continuous-time filter.
In general CTDS-ADCs, an input signal passes through n cascaded integrators (a continuous-time filter), and is quantized by a quantizer. A digital output of the quantizer is converted to an analog current signal by n D/A converters. Then, the analog current signal is fed back to the n integrators. In the CTDS-ADCs, an analog circuit portion includes no switches, so that a lower voltage can be possible. Moreover, a pre-filter usually required in using a sampling filter is not necessary in the CTDS-ADCs. Thus, the CTDS-ADCs are suited for applications to communication systems, and thus emphasis has been placed on their applied and development research in recent years.