Delta-sigma modulator and communication device
A delta-sigma modulator capable of outputting an output signal including a plurality of signals having different frequencies. The delta-sigma modulator includes: a plurality of input ports to which a plurality of input signals having different frequencies are inputted, respectively; a plurality of loop filters provided corresponding to the plurality of input ports, respectively; an adder configured to add outputs of the plurality of loop filters; and a quantizer configured to quantize an output of the adder. The plurality of loop filters each receive the input signal inputted to the corresponding input port and a feedback signal of an output of the quantizer. The plurality of loop filters each have a characteristic of stopping noise in the vicinity of a frequency of the input signal inputted to the corresponding input port.
1. A delta-sigma modulator comprising:
a plurality of input ports to which a plurality of input signals having different frequencies are inputted, respectively;
a plurality of loop filters provided corresponding to the plurality of input ports, respectively;
an adder configured to add outputs of the plurality of loop filters; and
a quantizer configured to quantize an output of the adder, wherein
the plurality of loop filters are each provided to receive the input signal inputted to the corresponding input port and a feedback signal of an output of the quantizer, and
the plurality of loop filters each have a characteristic of stopping noise in the vicinity of a frequency of the input signal inputted to the corresponding input port.
2. The delta-sigma modulator according to claim 1 , wherein
the plurality of loop filters each include:
a differentiator configured to calculate a difference between the input signal inputted to the corresponding input port and the feedback signal of the output of the quantizer; and
an inner filter to which an output of the differentiator is inputted.
3. The delta-sigma modulator according to claim 2 , wherein
the plurality of loop filters are each further provided with a feed forward path configured to add the input signal inputted to the corresponding input port, to an output of the inner filter.
4. A communication device comprising:
the delta-sigma modulator according to claim 1 ; and
one or a plurality of band-pass filters through which an output signal outputted from the quantizer of the delta-sigma modulator passes, wherein
the one or the plurality of band-pass filters have passbands which allows the plurality of input signals to the delta-sigma modulator to pass the band-pass filters.
5. The communication device according to claim 4 further including:
a frequency mixer to which the plurality of input signals having passed through the one or the plurality of band-pass filters are inputted, wherein
the plurality of input signals to the delta-sigma modulator include a local signal used for frequency conversion by the frequency mixer.