JP2014225922A - Δς modulator and communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ΔΣ modulator that outputs an output signal including a plurality of signals of different frequencies.SOLUTION: The ΔΣ modulator includes: a plurality of input ports 10a, 10b into which a plurality of input signals of different frequencies are input, respectively; a plurality of loop filters 11, 12 disposed in correspondence with the plurality of input ports, respectively; an adder 15 for adding up outputs of the plurality of loop filters; and a quantizer 16 for quantizing an output of the adder 15. The plurality of loop filters 11, 12 are each fed with the input signal input into the corresponding input port 10a, 10b and a feedback signal of an output of the quantizer 16. The plurality of loop filters 11, 12 each have the characteristic of rejecting noise about the frequency of the input signal input into the corresponding input port 10a, 10b.

Description

  The present invention relates to a ΔΣ modulator and a communication device.

The ΔΣ modulator includes a loop filter and a quantizer (see Non-Patent Document 1). The loop filter is a two-input system, and an input signal to the ΔΣ modulator is input to one input, and the output of the quantizer is fed back to the other input.
The output of the loop filter is given to the quantizer. The quantizer quantizes the output of the loop filter to generate an output signal (quantized signal) and outputs it.

Takao Wabo and Akira Yasuda (original author Richard Schreier, Gabor C. Temes) Introduction to ΔΣ analog / digital converters (Understanding Delta-Sigma Data Converters), Maruzen Corporation, 2007

The ΔΣ modulator is useful as a technique for outputting a radio signal using only a digital circuit.
Here, the present inventor has come up with the idea of using the ΔΣ modulation method when communication is performed using a plurality of bands simultaneously, such as a concurrent dual band. In this case, it is desirable that a single output signal output from one ΔΣ modulator can include a plurality of signals having different frequencies.
However, the conventional ΔΣ modulator is merely a one-input one-output system that performs ΔΣ modulation on one input signal and outputs one output signal, and cannot handle a plurality of input signals.

  Accordingly, an object of the present invention is to provide a ΔΣ modulator that can output an output signal including a plurality of signals having different frequencies.

(1) Viewed from one aspect, the present invention includes a plurality of input ports to which a plurality of input signals having different frequencies are respectively input, a plurality of loop filters provided corresponding to the plurality of input ports, and a plurality of input ports. An adder for adding the outputs of the loop filters, and a quantizer for quantizing the outputs of the adders, and each of the plurality of loop filters is input to a corresponding input port. And a feedback signal output from the quantizer, each of the plurality of loop filters is configured to block noise in the vicinity of the frequency of the input signal input to the corresponding input port. A delta-sigma modulator having

  According to the present invention, the quantizer can output an output signal including a plurality of signals having different frequencies.

(2) Each of the plurality of loop filters receives a differencer for obtaining a difference between an input signal input to the corresponding input port and a feedback signal of an output of the quantizer, and an output of the differencer. And an internal filter.

(3) Preferably, each of the plurality of loop filters further includes a feedforward path for adding the input signal input to the corresponding input port to the output of the internal filter. Since the input signal can be given to the quantizer side without doing so, the design of the loop filter becomes easy.

(4) From another viewpoint, the present invention provides the output signal output from the ΔΣ modulator according to any one of (1) to (3) and the quantizer of the ΔΣ modulator. 1 or a plurality of bandpass filters through which the signal passes, and the one or a plurality of bandpass filters is a communication device having a passband that allows each of the plurality of input signals to the ΔΣ modulator to pass therethrough.

(5) It further includes a frequency mixer to which a plurality of the input signals that have passed through one or a plurality of the bandpass filters are input, and the plurality of input signals to the ΔΣ modulator include a frequency by the frequency mixer. Preferably local signals used for the conversion are included. In this case, frequency conversion can be performed using a local signal included in the output signal of the ΔΣ modulator.

  According to the present invention, it is possible to output an output signal including a plurality of signals having different frequencies.

It is a block diagram of a dual band ΔΣ modulator. It is a block diagram of a ΔΣ modulator having a CRFB structure. FIG. 3 is a block diagram of an equivalent circuit of FIG. 2. (A) shows the positions of the zeros and poles of NTF ₁ , and (b) shows the positions of the zeros and poles of NTF ₂ . It is a figure which shows the frequency response of NTF. It is a diagram showing the frequency response of the STF ₁ and STF _2. It is the power spectrum which simulated the output of the dual band delta-sigma modulator. It is a power spectrum at 800 MHz of the output of the dual band ΔΣ modulator. It is a power spectrum in 1.5 GHz of the output of a dual band delta-sigma modulator. It is a power spectrum which shows the measurement result of the output of a dual band delta-sigma modulator. It is a block diagram of a generalized dual band ΔΣ modulator. It is a block diagram of a multiband ΔΣ modulator. It is the power spectrum of the output of a multiband delta-sigma modulator. It is a block diagram of the communication apparatus which concerns on a 1st example. It is a block diagram of the communication apparatus which concerns on a 2nd example. It is a block diagram of the communication apparatus which concerns on a 3rd example. It is a block diagram of the communication apparatus which concerns on a 4th example. It is a block diagram of the communication apparatus which concerns on a 5th example. It is a power spectrum of the output of the ΔΣ modulator according to the fifth example. It is a graph which shows the magnitude | size of a run length.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[1. First Embodiment: Dual Band ΔΣ Modulator]
FIG. 1 shows a ΔΣ modulator 1 according to this embodiment. The ΔΣ modulator 1 can receive two input signals U ₁ and U ₂ having different frequencies. The ΔΣ modulator 1 has two input ports (first input port 10a and second input port 10b) to which two input signals U ₁ and U ₂ are respectively input, and a single output port 10d. ing.
The output port 10d of the ΔΣ modulator 1 outputs a single output signal (quantized signal; ΔΣ modulation signal) including two input signals.

The ΔΣ modulator 1 illustrated in FIG. 1 includes a plurality of loop filters (first loop filter 11 and second loop filter 12), an adder 15, and a quantizer 16.
The number of loop filters 11 and 12 corresponding to the number of input ports 10a and 10b (two) is provided.
The plurality of loop filters 11 and 12 are respectively connected to the output side of the quantizer 16 via the first input portions 11a and 12a connected to the corresponding input ports 10a and 10b and the feedback paths 18a and 18b. 2nd input part 11b, 12b.

Input signals U ₁ and U ₂ input to the corresponding input ports 10a and 10b are input to the first input units 11a and 12a. The feedback signal V of the output V of the quantizer 1 is input to the second input units 11b and 12b.

The plurality of loop filters 11 and 12 include differentiators 110a and 120a, respectively. The first and second paths 110d and 120d connected to the first input units 11a and 12a and the second paths 110e and 120e connected to the second input units 11b and 12b are connected to the differentiators 110a and 120a, respectively. Has been. The differentiators 110a and 120a obtain differences U ₁ −V and U ₂ −V between the input signals U ₁ and U ₂ and the feedback signal V from the quantizer 16, respectively.

Differences U ₁ −V and U ₂ −V obtained by the differentiators 110 a and 120 a are input to internal filters 110 b and 120 b provided in the loop filters 11 and 12. The transfer function of the internal filter 110b of the first loop filter 11 is expressed as L ₁ (z), and the transfer function of the internal filter 120b of the second loop filter 11 is expressed as L ₂ (z).

The outputs L ₁ (z) (U ₁ (z) −V (z)) and L ₂ (z) (U ₂ (z) −V (z)) of the internal filters 110 b and 120 b 12 is provided to the adders 110c and 120c provided in FIG.
Feed forward paths 110f and 120f for inputting the input signals U ₁ and U ₂ input to the first input units 11a and 12a to the adders 110c and 120c are connected to the adders 110c and 120c. Therefore, each adder 110c, 120c receives the input signals U1, U2 and the outputs L ₁ (z) (U ₁ (z) -V (z)), L ₂ (z) (U ₂ ) of the internal filters 110b, 120b. (Z) −V (z)).

Outputs of the adders 110c and 120c (outputs of the loop filters 11 and 12) Y ₁ and Y ₂ are added by the adder 15. In the present embodiment, three two-input adders 15, 110c, and 120c are used, but one four-input adder may be used instead of the three two-input adders 15, 110c, and 120c. .

  The output Y of the adder 15 is given to the quantizer 16. The quantizer 16 of the present embodiment is a two-level quantizer and outputs a 1-bit pulse train as a quantized signal (ΔΣ modulation signal) V. This quantized signal V becomes an output signal of the ΔΣ modulator 1. The output signal V is given to the loop filters 11 and 12 via the feedback paths 18a and 18b.

Now, in order to facilitate understanding of the ΔΣ modulator 1 (multiple input one output system) shown in FIG. 1, a conventional ΔΣ modulator (one input one output system) will be described.
Conventional ΔΣ modulators include a low-pass ΔΣ modulator and a band-pass delta-sigma modulator. The low-pass ΔΣ modulator refers to the one whose quantization noise stop band is centered at the frequency zero, and the band-pass ΔΣ modulator refers to the one whose center is the quantization noise stop band in a desired frequency band other than zero. The noise transfer function NTF of the bandpass ΔΣ modulator has a characteristic of suppressing quantization noise in a desired frequency band by a bandstop filter.

In the low-pass ΔΣ modulator, the zero point of the noise transfer function NTF (z) (Noise Transfer Function) is near the frequency zero (z = 1) on the unit circle, and the band-pass ΔΣ modulator is the zero point of the noise transfer function NTF. Is at a position other than the frequency zero (z = 1) on the unit circle.
Therefore, in order to obtain a bandpass ΔΣ modulator that operates with respect to an input signal in a desired band, the zeros and poles in the noise transfer function NTF of the lowpass ΔΣ modulator are moved to positions on the unit circle corresponding to the desired band. Rotate.

Therefore, first, the low-pass ΔΣ modulator will be described below. FIG. 2 shows a low-pass delta-sigma modulator (second non-patent document 1) having a second-order CRFB (cascade of resonators with distributed feedback) structure.
The CRFB low pass ΔΣ modulator has a low distortion mode. In this low distortion mode, in FIG. 2, a1 = b1, a2 = b2, b3 = 1, and the signal transfer function (Signal Transfer Function) STF (z) = 1 of the ΔΣ modulator. Therefore, the output V (z) of the ΔΣ modulator shown in FIG. 2 is simplified as the following equation (1). U (z) is the input of the ΔΣ modulator, and E (z) is the quantization noise of the ΔΣ modulator.

here,

FIG. 3 shows an equivalent circuit of the ΔΣ modulator shown in FIG. Therefore, the output V (z) of the ΔΣ modulator shown in FIG.
The ΔΣ modulator shown in FIG. 3 is simpler than the circuit shown in FIG. In the ΔΣ modulator shown in FIG. 3, the difference unit 101 obtains the difference U (z) −V (z) between the input signal U (z) and the output signal V (z), and the difference U (z) −V. (Z) is given to the filter 102 indicated by the transfer function L (z). The output L (z) (U (z) −V (z)) of the filter 102 is given to the adder 103. The adder 103 is directly input with the input signal U (z).

The transfer function L (z) of the filter 102 in FIG. 3 is expressed by using the noise transfer function NTF (z) of the ΔΣ modulator as shown in the following equation (3). The noise transfer function NTF (z) has a characteristic (band stop characteristic or high-pass characteristic) that suppresses quantization noise in the frequency band of the input signal of the ΔΣ modulator.

The configuration of each of the plurality of loop filters 11 and 12 shown in FIG. 1 corresponds to the configuration (configuration as a loop filter) in a range surrounded by a dotted line denoted by reference numeral 100 in FIG.
That is, the ΔΣ modulator 1 shown in FIG. 1 is a combination of a plurality of conventional ΔΣ modulators so that a quantizer is shared. The combination of a plurality of conventional ΔΣ modulators may be a combination of a plurality of bandpass ΔΣ modulators having different noise rejection bands, or a combination of a bandpass ΔΣ modulator and a low-pass ΔΣ modulator. There may be.

The filter (internal filter) 110b of the first loop filter 11 corresponding to the filter 102 (transfer function L (z)) in FIG. 3 is a transfer function L ₁ (shown using the first noise transfer function NTF ₁ (z). z). The first noise transfer function NTF ₁ (z) is a characteristic (band stop) that suppresses quantization noise at the carrier frequency (first frequency) f1 of the first input signal U ₁ (z) input to the first loop filter 11. Characteristic).

Similarly, the filter (internal filter) 120b of the second loop filter 12 corresponding to the filter 102 (transfer function L (z)) of FIG. 3 has a transfer function L ₂ indicated by using the second noise transfer function NTF ₂ (z). (Z) The second noise transfer function NTF ₂ (z) suppresses quantization noise at the carrier frequency (first frequency) f2 of the second input signal U ₂ (z) input to the second loop filter 12 (band stop characteristic). It has the characteristic to do.

The output signal V (z) of the ΔΣ modulator 1 in FIG. 1 is expressed as the following equation (4). In Equation (4), STF ₁ (z) is a first signal transfer function for the first input signal U ₁ (z), and STF ₂ (z) is for the second input signal U ₂ (z). The second signal transfer function, NTF (z) is a noise transfer function in the entire ΔΣ modulator.

here,

Hereinafter, an example in which the first frequency f1 of the first input signal U ₁ (z) is 800 MHz and the second frequency f2 of the second input signal U ₂ (z) is 1.5 GHz will be described. Each of the loop filters 11 and 12 has a sixth-order (M = 6) CRFB structure. The sampling frequency fs of the ΔΣ modulator 1 is 3.9 GHz.

Since the frequency f1 of the first input signal U ₁ (z) is 800 MHz, the first noise transfer function NTF ₁ (z) of the first loop filter 11 to which the first input signal U ₁ (z) is input is The center of the noise stop band is set to be approximately 800 MHz. Specifically, as shown in FIG. 4A, the zero (Zero) z _xi and the pole (Pole) p _xi are present in the vicinity of 800 MHz (fs / 4 = about 1 GHz slightly before the unit circle) on the unit circle. Set to

Further, since the frequency f2 of the second input signal U ₂ (z) is 1.5 GHz, the second noise transfer function NTF ₂ (2) of the second loop filter 12 to which the second input signal U ₂ (z) is input. z) is set so that the center of the noise stopband is approximately 1.5 GHz. Specifically, as shown in FIG. 4B, the zero (Zero) z _xi and the pole (Pole) p _xi are around 1.5 GHz on the unit circle (fs / 4 = about 1 GHz and fs / 2 = Between about 2 GHz).
It should be noted that all variables for determining NTF ₁ (z) and NTF ₂ (z) are determined by zero (Zero) z _xi and pole (Pole) p _xi as shown in Equation (10) ( (See Non-Patent Document 1 for zero and pole optimization).

When the first noise transfer function NTF ₁ (z) and the second noise transfer function NTF ₂ (z) are set as described above, the noise transfer function NTF (z) of the ΔΣ modulator 1 is as shown in FIG. Become.
As is clear from FIG. 5, the noise transfer function NTF (z) corresponds to two frequencies (dual band) of 800 MHz and 1.5 GHz, corresponding to two stop bands (notches) near 800 MHz and 1.5 GHz. ).
Therefore, the quantization noise shifts outside these two stop bands, and the quantization noise is suppressed within these two stop bands (noise shaping).

FIG. 6 shows the first signal transfer function STF ₁ (z) and the second signal transfer when the first noise transfer function NTF ₁ (z) and the second noise transfer function NTF ₂ (z) are set as described above. The function STF ₂ (z) is shown.
As is clear from FIG. 6, the first signal transfer function STF ₁ (z) for the first input signal U ₁ (z) = 800 MHz hardly attenuates the signal in the band near 800 MHz (pass band), There is a stop band (notch) in the vicinity of 1.5 GHz which is the frequency of the second input signal U ₂ (z).
Further, the second signal transfer function STF ₂ (z) for the second input signal U ₂ (z) = 1.5 GHz hardly attenuates the signal in the band near 1.5 GHz (pass band). There is a stop band (notch) in the vicinity of 800 MHz, which is the frequency of the input signal U ₁ (z).

  FIG. 7 shows a power spectrum (simulated power spectrum) of the output V (z) of the ΔΣ modulator 1 of FIG. As shown in FIG. 7, an 800 MHz signal and a 1.5 GHz signal are output, and stop bands are formed in the vicinity of 800 MHz and 1.5 GHz. Within these stop bands, quantization noise is sufficiently suppressed.

Therefore, in the ΔΣ modulator 1 of FIG. 1, even if a plurality of input signals U ₁ (z) and U ₂ (z) having different frequencies are input simultaneously, the input signals U ₁ (z) and U ₂ (z) Without interfering with each other, a plurality of input signals U ₁ (z) and U ₂ (z) can be simultaneously included in a single output signal V (z) and output.

8 to 10 show actual measurement results when 800 MHz and 1.5 GHz long term evolution (LTE) signals having a bandwidth of 5 MHz are used as two input signals U ₁ and U ₂ to the ΔΣ modulator 1. ing.
FIG. 8 shows a power spectrum in the vicinity of 800 MHz in the 1-bit digital data stream (3.9 Gbps) that is the output V of the ΔΣ modulator 1, and it can be seen that the ACLR is about 50 dBm.
FIG. 9 shows a power spectrum in the vicinity of 1.5 GHz in the 1-bit digital data stream (3.9 Gbps) that is the output V of the ΔΣ modulator 1, and it can be seen that the ACLR is about 48 dBm.
FIG. 10 shows an overall image of the power spectrum of the output V of the ΔΣ modulator 1.

As is apparent from FIGS. 7 to 10, the spectrum of the output V of the ΔΣ modulator 1 in FIG. 1 is good as the spectrum of the RF signal.
Therefore, the ΔΣ modulator 1 of FIG. 1 is suitable for outputting a plurality of RF signals as a 1-bit digital data stream.

[2. Second Embodiment: Generalized ΔΣ Modulator Structure]
The structure of each loop filter 11, 12 of the ΔΣ modulator 1 is an example, and is not limited to the structure shown in FIG. 1, and various loop filters in a conventional one-input one-output ΔΣ modulator can be adopted. The structure can be adopted as a multiple 11 or 12 structure with each loop of the ΔΣ modulator 1.
FIG. 11 shows a ΔΣ modulator 1 in which the loop filters 11 and 12 are generalized.

The characteristics of the first loop filter in FIG. 11 are expressed using LA ₁ (z) and LB ₁ (z) instead of L1 (z) in FIG. The characteristics of the second loop filter in FIG. 11 are expressed using LA ₂ (z) and LB ₂ (z) instead of L ₂ (z) in FIG. These transfer functions LA ₁ (z), LB ₁ (z), LA ₂ (z), and LB ₂ (z) will be described later.
The other points are the same as in FIG.

[3. Third Embodiment: Multiband Compatible ΔΣ Modulator]
FIG. 12 shows the multiband ΔΣ modulator 1 that can input _three input signals U ₁ , U ₂ , and U ₃ having different frequencies.
The ΔΣ modulator 1 of FIG. 12 includes a third loop filter 13 corresponding to the third input signal U ₃ in addition to the first loop filter 11 and the second loop filter 12 similar to the ΔΣ modulator 1 of FIG. Yes. The third loop filter is provided corresponding to the third input port 10c of the third input signal U ₃ is input, basically, similar to the first loop filter 11 and a second loop filter 12 configuration Have.
That is, the third loop filter 13 includes a first input unit 13a connected to the third input port 10c, and a second input unit 13b connected to the output side of the quantizer 16 via the third feedback path 18c. It is equipped with.
Further, the third loop filter 13 includes a subtractor 130a, an internal filter 130b, an adder 103c, a feedforward path 130f, and the like.

The adder 15 of FIG. 12 adds the outputs Y ₁ , Y ₂ , Y ₃ of the _three loop filters 11, 12, 13 and gives them to the quantizer 16.
The output V of the quantizer 16 is fed back to the second input sections 11b, 12b, and 13b of the three loop filters 11, 13, and 13, respectively.

The output V of the ΔΣ modulator 1 in FIG. 12 is expressed by the following equation (11) (when N = 3 in equation (11)). In Expression (11), STF _i (z) is an i-th signal transfer function for the i-th input signal U _i (z). Note that the number N of input signals that can be input to the ΔΣ modulator 1 is not limited to 2 or 3, and may be 4 or more.

here,

FIG. 13 shows a case where 800 MHz, 1.5 GHz, and 500 MHz long term evolution (LTE) signals having a bandwidth of 5 MHz are three input signals U ₁ , U ₂ , U ₃ to the ΔΣ modulator 1. A power spectrum (simulated power spectrum) of the output V (z) of the ΔΣ modulator 1 is shown.
The first noise transfer function NTF ₁ (z) of the first loop filter 11 is set so as to correspond to the frequency (800 MHz) of the first input signal U ₁ so that the center of the noise stop band is approximately 800 MHz. did.
Further, the second noise transfer function NTF ₂ (z) of the second loop filter 12 corresponds to the frequency (1.5 GHz) of the second input signal U ₂ , and the center of the noise stop band is approximately 1.5 GHz. Was set to be.
Further, the third noise transfer function NTF ₃ (z) of the third loop filter 13 is set so as to correspond to the frequency (500 MHz) of the third input signal U ₃ so that the center of the noise stop band is approximately 500 MHz. did.

As shown in FIG. 13, a 500 MHz signal, an 800 MHz signal, and a 1.5 GHz signal are output, and stop bands are formed near 500 MHz, 800 MHz, and 1.5 GHz. Within these stop bands, quantization noise is sufficiently suppressed.
Thus, good results are obtained even when the number of input signals is set to three.

[4. Generalized ΔΣ modulator output]
As described above, the number of the plurality of loop filters in the above-described ΔΣ modulator 1 is not particularly limited.
Therefore, when the generalized ΔΣ modulator 1 shown in FIG. 11 has an arbitrary number of loop filters, the output of such ΔΣ modulator 1 is the transfer function LA _i , LB _{i of} each loop filter. Is expressed as follows. Note that LA _i and LB _i are transfer functions of the i-th loop filters 11 and 12, and N is the number of input signals (loop filters).

From the above equation, the transfer functions LA _i and LB _i of the i-th loop filters 11 and 12 can be obtained by calculation if the desired signal transfer function STFi noise transfer function NTFi is determined for each corresponding i-th input signal. it can. Since this calculation is equivalent to the calculation in the loop filter in the conventional one-input one-output ΔΣ modulator, it can be easily calculated.

As shown in FIG. 1, each of the loop filters 11 and 12 inputs only the difference U (z) −V (z) between the input signal U (z) and the feedback signal V (z) to the internal filters 110b and 120b. And having the feed forward paths 110f and 120f, the transfer functions LA _i and LB _i are as follows:
LA _i (z) = L _i (z) +1
LB _i (z) = − L _i (z)
Holds.

Moreover, when each loop filter 11 and 12 of FIG. 1 does not have the feedforward paths 110f and 120f,
LA _i (z) = L _i (z)
LB _i (z) = − L _i (z)
Holds.

As described above, when the internal filters 110b and 120b are input to which only the difference U (z) −V (z) between the input signal U (z) and the feedback signal V (z) is input, Since only one transfer function L _i (z) needs to be determined, the design is facilitated.

Further, when the feedforward paths 110f and 120f are provided as shown in FIG. 1, the input signal U _i (z) to be output is directly transmitted to the quantizer side without passing through the internal filters 110b and 120b. Since it can be given, the design becomes easy.

[5. Communication device]
[5.1 First Example of Communication Device]
FIG. 14 shows a first example of a communication device (wireless communication device) 200 using the ΔΣ modulator 1 according to the above-described embodiment.
The communication device 200 includes a plurality of quadrature modulation units (primary modulators) 21 and 22, a ΔΣ modulator (secondary modulator) 1, and a band-pass filter 25.
The plurality of quadrature modulation units 21 and 22 perform quadrature modulation as primary modulation on the baseband signals I ₁ , Q ₁ , I ₂ , and Q ₂ , respectively. The plurality of orthogonal modulation units 21 and 22 output radio signals (RF signals) U ₁ and U ₂ having different frequencies because the frequencies w ₁ and w ₂ of the local transmitters 21a and 22a are different from each other.
The plurality of radio signals U ₁ and U ₂ are input signals to the ΔΣ modulator 1.

ΔΣ modulator 1, for a plurality of radio signals U _1, U _2, performs ΔΣ modulation as secondary modulation, and outputs a pulse signal including a plurality of radio signals U _1, U _2. The output signal of the ΔΣ modulator 1 is given to the band pass filter 25 via the transmission path 24. The band pass filter 25 has a pass band that allows a plurality of radio signals U ₁ and U ₂ to pass through. The band-pass filter 25 removes noise outside the bands of the plurality of radio signals U ₁ and U ₂ .
When the frequencies of the plurality of radio signals U ₁ and U ₂ are close to each other, even if the plurality of radio signals U ₁ and U ₂ are output from the ΔΣ modulator ₁ , the bandpass filter 25 As shown in FIG.

The plurality of radio signals U ₁ and U ₂ output from the band pass filter 25 are amplified by the power amplifier 31 and output from the antenna 32.
The communication apparatus 200 can operate in a dual band mode (multiband mode) in which a plurality of radio signals having different frequencies are output simultaneously.
Further, since the output of the ΔΣ modulator 1 is a digital signal, it is possible to transmit a radio signal as a digital signal to a long distance through a high-speed transmission path 24 such as an optical fiber.
In addition, since a plurality of radio signals can be included in one digital data stream, a plurality of radio signals can be transmitted through one transmission path 24.

[5.2 Second Example of Communication Device]
FIG. 15 shows a second example of a communication device (wireless communication device) 200 using the ΔΣ modulator 1 according to the above-described embodiment.
In the communication device 200 according to the second example, a plurality (two) of band-pass filters 25 and 26 are provided corresponding to the number of radio signals ₁ and U ₂ . The output of the ΔΣ modulator 1 is given to the plurality of bandpass filters 25 and 26 via the transmission line 24.

When the frequencies of the plurality of radio signals U ₁ and U ₂ are separated, a plurality of band pass filters 25 and 26 having pass bands corresponding to the frequencies of the respective radio signals U ₁ and U ₂ are used. Noise outside the band of the radio signals U ₁ and U ₂ can be appropriately removed.
Other points are the same as in FIG. In FIG. 15, the circuits after the bandpass filters 25 and 26 are omitted.

[5.3 Third Example of Communication Device]
FIG. 16 shows a third example of a communication device (wireless communication device) 200 using the ΔΣ modulator 1 according to the above-described embodiment.
The communication device 200 according to the third example is provided with a frequency mixer (frequency converter) 28 on the output side of one band pass filter 26 of the communication device 200 according to the second example. In the third example, the other points are the same as in the second example.

  In the third example, the signal (frequency w1) output from the first orthogonal modulation unit 21 is a radio frequency signal (RF signal), and the signal (frequency w2) output from the second orthogonal modulation unit 22 is compared. This is an intermediate frequency signal (IF signal) having a low target frequency.

  In the third example, the IF signal output from the bandpass filter 26 is subjected to frequency conversion by the frequency mixer 28 and converted to an RF signal of w2 + w3 (w3 is the frequency of the local oscillator 29).

By performing frequency conversion on the output side of the ΔΣ modulator 1 while keeping the frequency of the input signal to the ΔΣ modulator 1 low, the operating frequency (sampling frequency) of the ΔΣ modulator 1 can be suppressed low.
In FIG. 16, only one of the plurality of input signals is an IF signal, but both may be IF signals.

[5.4 Fourth Example of Communication Device]
FIG. 17 shows a fourth example of a communication device (wireless communication device) 200 using the ΔΣ modulator 1 according to the above-described embodiment.
In the fourth example, the output signal (IF signal; frequency w1) of the quadrature modulation unit 21 is input to one input port of the ΔΣ modulator 1, whereas the other input port is used for frequency conversion. The local signal (local oscillation signal; frequency w2) is input.

The ΔΣ modulator 1 of the fourth example outputs a digital signal including an IF signal having a frequency w1 and a local signal having a frequency w2.
These signals are input to a frequency mixer (frequency converter) 28 after noise is removed by the bandpass filters 25 and 26. The frequency mixer 28 converts the IF signal having the frequency w1 into an RF signal having the frequency w1 + w2.

As in the communication device 200 of the fourth example, the IF signal is input to the ΔΣ modulator 1 instead of the RF signal, so that the operating frequency (sampling frequency) of the ΔΣ modulator 1 can be kept low.
Moreover, since the local signal for frequency conversion is also included in the output of the delta-sigma modulator 1 which is a digital signal, the analog circuits after the BPFs 25 and 26 do not need to have a local oscillator, and the configuration is simplified. Can do.

[5.5 Example of Communication Device]
FIG. 18 shows a fifth example of a communication device (wireless communication device) 200 using the ΔΣ modulator 1 according to the above-described embodiment.
In the fifth example, the output signal (frequency w1) of the quadrature modulation unit 21 is input to one input port of the ΔΣ modulator 1, while nothing is input to the other input port.
Of the two loop filters 11 and 12 of the ΔΣ modulator 1, the loop filter corresponding to the input port to which the output signal of the quadrature modulation unit 21 is input has the center of its noise prevention band and the frequency w 1 of the output signal. Is set to be
On the other hand, in the loop filter corresponding to the input port that has no input, the center of the noise stopband is set near zero frequency (high-pass filter).

FIG. 19 shows the power spectrum of the output of the ΔΣ modulator 1 when the frequency w1 of the output signal of the quadrature modulation unit 21 is 1.5 G in FIG.
As is clear from FIG. 19, the output of the ΔΣ modulator 1 includes a 1.5 GHz signal, but there is no signal at a frequency of zero. However, noise is suppressed both in the vicinity of 1.5 GHz and in the vicinity of 0 Hz.

As described above, according to the fifth example, the ΔΣ modulator 1 can output an output signal including a signal having a specific frequency and having a small DC component (frequency zero signal).
If the DC component is reduced in the output signal of the ΔΣ modulator 1, the run length can be reduced.
That is, as shown in FIG. 20, the number of consecutive 0s (see FIG. 20 (a)) or 1 (see FIG. 20 (b)) in the pulse signal is suppressed to about 2 to 4, and the run length is small. You can see that
By reducing the run length, the distortion of the pulse signal can be suppressed. Therefore, in the fifth example, distortion of the output signal (pulse signal) of the ΔΣ modulator 1 can be suppressed.

  In the fifth example, a signal with little signal and noise was obtained in the vicinity of the frequency zero. However, by setting the center of the noise prevention band of the loop filter that has no input to the desired frequency, the signal is obtained in the vicinity of the desired frequency. A signal with less noise can be obtained.

[6. Addendum]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 ΔΣ modulator 10a, 10b, 10c Input port 10d Output port 11 First loop filter 110a Difference unit (adder)
110b Internal filter (filter)
110c Adder 110f Feed forward path 12 Second loop filter 120a Differentiator (adder)
120b Internal filter (filter)
120c Adder 120f Feed forward path 13 Third loop filter 130b Internal filter (filter)
130c Adder 130f Feedforward path 15 Adder 16 Quantizers 18a, 18b, 18c Feedback path

Claims (5)

A plurality of input ports to which a plurality of input signals having different frequencies are respectively input;
A plurality of loop filters provided corresponding to each of the plurality of input ports;
An adder for adding the outputs of the plurality of loop filters;
A quantizer for quantizing the output of the adder;
With
Each of the plurality of loop filters is provided so that an input signal input to the corresponding input port and a feedback signal of an output of the quantizer are input.
Each of the plurality of loop filters has a characteristic of blocking noise near the frequency of the input signal input to the corresponding input port. Each of the plurality of loop filters is
A differentiator for determining a difference between a corresponding input signal input to the input port and an output feedback signal of the quantizer;
An internal filter to which the output of the differentiator is input;
The ΔΣ modulator according to claim 1. The ΔΣ modulator according to claim 2, wherein each of the plurality of loop filters further includes a feedforward path that adds an input signal input to the corresponding input port to an output of the internal filter. The ΔΣ modulator according to any one of claims 1 to 3,
One or a plurality of bandpass filters through which an output signal output from the quantizer of the ΔΣ modulator passes;
With
One or a plurality of the bandpass filters have a pass band that allows each of the plurality of input signals to the ΔΣ modulator to pass therethrough. A frequency mixer that receives a plurality of the input signals that have passed through the plurality of bandpass filters;
The communication apparatus according to claim 4, wherein the plurality of input signals to the ΔΣ modulator include a local signal used for frequency conversion by the frequency mixer.