JPH0998194A - Orthogonal modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an orthogonal modulator with which a carrier frequency can be changed in configuration using no multiplier. SOLUTION: The data of a base band signal are interpolated by increasing a sampling rate up to the frequency of a clock while respectively passing the signals of I channel and Q channel through digital low-pass filters 2 and 3 to be operated by the clock at an N-fold (N: natural number) frequency as high as the sampling frequency of the base band signal. The interpolated data are modulated by the carrier at the 1/4 frequency of a clock frequency while alternately selecting the data of I channel and the data of Q channel by a multiplexer 4 and controlling a code by a code control part 5. The modulated data are converted to analog data by a D/A converter 6 and outputted while passing only the band of carrier frequency through a band pass filter 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature modulator that puts a baseband signal on a carrier frequency.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional quadrature modulator that changes a carrier frequency. In FIG. 2, reference numeral 8 is an oscillator for generating a clock having a frequency N times (N: natural number) the sampling frequency of the baseband signal. Reference numeral 9 is a digital oscillator that generates a carrier, and can change the oscillation frequency. Reference numerals 10 and 11 are digital low-pass filters that pass only the low-frequency component of the baseband signal in synchronization with the clock. Reference numeral 14 is a phase delay device that delays the phase of the carrier by π / 2. Reference numerals 12 and 13 denote multipliers that put the signal output from the digital low-pass filter on a carrier. Reference numeral 15 is an adder, which is I channel and Q
Combines the data output from the channel filters.
A D / A converter 16 converts the digital data output from the adder to analog. Reference numeral 17 is a bandpass filter that passes only the carrier frequency band.

The operation of the quadrature modulator having the above structure will be described below. First, the sampling rate is raised to the frequency of the clock by passing the I-channel and Q-channel signals to the digital low-pass filters 10 and 11 operating with a clock having a frequency N times (N: a natural number) the sampling frequency of the baseband signal. Interpolate band signal data. next,
The Q-channel signal is placed on the carrier generated by the digital oscillator 9 and the I-channel signal is transferred to the Q-phase by the phase delay unit 14.
The carrier of which the phase is delayed so as to have an orthogonal relationship with the carrier of the channel is placed, and the data of the respective channels are combined by the adder 15. This is converted to analog by the D / A converter 16 and output through the bandpass filter 17 that passes only the carrier frequency band. When changing the carrier frequency, the oscillation frequency of the digital oscillator 9 that generates the carrier is directly changed.

[0004]

In the conventional configuration, since the carrier frequency is directly changed by the digital oscillator, a multiplier operating at the same frequency as the sampling frequency after interpolation is required.

An object of the present invention is to provide a quadrature modulator capable of changing a carrier frequency without using a multiplier.

[0006]

In order to achieve the above object, the quadrature oscillator of the present invention is an oscillator which generates a clock having a variable oscillation frequency and a frequency N times (N: natural number) the sampling frequency of a baseband signal. A first digital low-pass filter having a variable filter coefficient and passing only the low-frequency component of the I-channel signal of the baseband signal in synchronization with the oscillator clock; and a variable filter coefficient for the oscillator clock. A second digital low-pass filter that synchronously passes only the low-pass component of the Q-channel signal of the baseband signal; and a multiplexer that selects the outputs of the first and second low-pass filters in synchronization with the clock of the oscillator. A code control unit for controlling the code of the data output from the multiplexer in synchronization with the oscillator A.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the above configuration, assuming that the carrier frequency is 1/4 of the clock frequency, the I channel carriers are 1,0, -1,0,1, ..., The Q channel carriers are 0, -1. , 0, 1, 0, ..., so I channel and Q
By alternately selecting the channel data and controlling the code of the data, the baseband signal is placed on the carrier. From the above, a digital oscillator for carrier generation is unnecessary, and thus a multiplier for loading the baseband signal on the carrier is unnecessary. When changing the carrier frequency, the clock frequency and the coefficient of the digital low-pass filter are changed.

[0008]

EXAMPLES An example of the present invention will be described below.

FIG. 1 is a block diagram of a quadrature modulator of the present invention. In the figure, 1 is an oscillator that generates a clock having a variable oscillation frequency and a frequency N times (N: a natural number) the sampling frequency of a baseband signal, and 2 and 3 are low-frequency components of the baseband signal with variable filter coefficients Digital low-pass filter that only passes through, 4 is a multiplexer,
Reference numeral 5 is a code control unit, 6 is a D / A converter, and 7 is a bandpass filter that passes only the carrier frequency band. The operation of the quadrature modulator configured as above will be described below.

First, the sampling frequency is raised to the clock frequency through the digital low-pass filters 2 and 3 operating with a clock having a frequency N times (N: a natural number) the sampling frequency of the baseband signal through the I-channel and Q-channel signals, respectively. , Interpolate the data of the baseband signal. The interpolated baseband signal data at this time are designated as I _n and Q _n . Next, the multiplexer 4
The data after the channel interpolation and the data after the Q channel interpolation are selected alternately. Selected data I ₁ , Q ₂ ,
The signs of I ₃ , Q ₄ , ... Are I ₁ , -Q ₂ , -I ₃ , Q ₄ ,
The baseband signal is modulated by the carrier having a frequency of ¼ of the clock frequency by controlling the code control unit 5 so that The modulated data is converted into analog by the D / A converter 6, and the band pass filter 7 passes only the carrier frequency band and outputs it. When changing the carrier frequency, the clock frequency of the oscillator 1 is changed to four times the desired carrier frequency, and the coefficients of the digital low-pass filters 2 and 3 are changed accordingly.

[0011]

As described above, according to the quadrature modulator of the present invention, the carrier frequency is set to 1/4 of the clock frequency,
By using the multiplexer and the code control unit, the multiplier that was required in the conventional quadrature modulator that changes the carrier frequency is unnecessary, and the oscillator with the variable oscillation frequency and the digital low-pass filter with the variable filter coefficient are used. As a result, the carrier frequency can be changed.

[Brief description of drawings]

FIG. 1 is a block diagram of a quadrature modulator according to an embodiment of the present invention.

FIG. 2 is a block diagram of a quadrature modulator in a conventional example.

[Explanation of symbols]

 1 Oscillator 2, 3 Digital low-pass filter 4 Multiplexer 5 Code control unit 6 D / A converter 7 Band-pass filter

Claims (1)

[Claims] 1. An oscillator having a variable oscillation frequency and generating a clock having a frequency N times (N: a natural number) the sampling frequency of a baseband signal, and a baseband synchronized with the clock of the oscillator with a variable filter coefficient. A first digital low-pass filter that passes only the low-pass component of the I-channel signal of the signal, and a low-pass component of the Q-channel signal of the baseband signal that passes in synchronization with the clock of the oscillator with a variable filter coefficient. A second digital low-pass filter, a multiplexer that selects the outputs of the first and second low-pass filters in synchronization with the clock of the oscillator, and a sign of data output from the multiplexer in synchronization with the oscillator. And a D / A converter for converting the output from the code control unit from digital to analog , Quadrature modulator comprising a bandpass filter which passes only the band of the carrier frequency of the modulated signal outputted from the D / A converter.