JPH0234539B2 - DEIJITARUSHORIGATACHOTSUKOHENCHOSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an improvement in a digitally processed quadrature modulation device.

(Prior Art) Conventionally, a digital processing type quadrature modulation device that limits the band of two different types of baseband signals using digital low-pass filters, amplitude modulates them using mutually orthogonal carrier waves, and adds them is shown in Fig. 1. The structure was as shown.

FIG. 1 is a block diagram showing an example of the configuration of this type of device, which has been well known in the past, and includes digital low-pass filters 1-1, 1-2, a multiplier circuit 2-
1, 2-2, an adder circuit 3, and a sine wave oscillator 4 that generates two orthogonal outputs, in other words mutually orthogonal carrier waves, and outputs them to the multiplier circuits 2-1, 2-2.

However, in the conventional configuration as shown in Fig. 1, the number of circuits including the multiplier circuit, the adder circuit, and the sine wave oscillator is large, resulting in an expensive price and a large mounting area. It was hot.

(Object of the Invention) The present invention has been made in consideration of the above points, and is configured without using conventional multiplier circuits, adder circuits, sine wave oscillators, etc., and is inexpensive and miniaturized. An object of the present invention is to provide a digitally processed quadrature modulation device.

(Structure of the Invention) In other words, the present invention provides a device of this type that includes first and second filters that are connected to a baseband signal and operate at different sample phases, and that scans the outputs of both filters in a time-divisional manner. A digital-to-analog converter, a digital-to-analog converter, and a bandpass filter are connected in sequence, and this configuration achieves the above object. The present invention will be explained below using the drawings.

(Embodiment of the Invention) FIG. 2 is a block diagram showing an embodiment of the digital processing type quadrature modulation device according to the present invention.
receive input signals a and b, respectively, and sample by driving sample pulses c and d of different phases,
Send out outputs e and f. When the switching circuit 6 which performs switching scanning in a time-division manner receives the outputs e and f, it creates an output g by the switching scanning and sends it out. This output g is sent to a digital-to-analog converter 7, which converts the digital signal into an analog signal and sends out an output h, which is then orthogonally modulated by an analog bandpass filter 8 to produce an output i signal. Send.

FIG. 3 is a time chart illustrating the operation of the digitally processed orthogonal modulator described above.
S in the figure is a time reference for explanation. Furthermore, the period T of the sample pulses c and d for driving the digital low-pass filter is selected to be the reciprocal of the carrier wave frequency c, and is set to T=1/c. These sample pulses c and d have a phase difference of T/4 here, and therefore, in the switching circuit 6, the output e is output when the time reference is A, and the output f is output when the time reference is B.
The configuration is such that an output g, in other words, an output h, which outputs a no-signal level output is obtained when the time reference is C or D.

FIG. 4 is an explanatory diagram of the operation of the digital processing type orthogonal modulation device having the above configuration using a frequency spectrum. In the figure, e and f indicate the frequency spectrum of the digital low-pass filter output, and e′,
f' is a vector indicating the phase of the carrier wave. or,
i' indicates the transmission characteristic of the analog bandpass filter, and i indicates the spectrum of the orthogonal modulated signal by the analog bandpass filter.

Here, as shown in FIG. 4, it is clear that the present invention uses sample pulses with different phases to obtain two orthogonal carrier waves.
This will be explained below. The signals e and f are each expressed as follows (1)
It can be shown by equation (2).

e=(ap)・{ _∞ 〓 ^n=-∞ δ(t・nT)} =(ap)・{1+cosωct+cos2ωct+……}
……(1) f=(bp)・{ _∞ 〓 ^n=-∞ δ(t+T/4−nt)} =(bp)・{1+cos(ωct+2π/4) +cos(2ωct+4π/4+……} ……( 2) However, above T = 2π/ωc, in equations (1) and (2), if you pay attention to the second term in { }, it is clear that the two carrier waves are orthogonal. This is illustrated in Figure 4.

In addition, in the above formula, the convolution integral is shown, and p
is the impulse response of the digital low-pass filter.

(Effects of the Invention) As detailed above, according to the present invention, in this type of device, two types of different sample phases are prepared, a digital low-pass filter is driven, and the output is obtained by switching. Therefore, conventional multiplier circuits, adder circuits, and sine wave oscillators are no longer required.
Therefore, it is possible to expect an excellent effect of providing a digitally processed quadrature modulation device which is inexpensive and can be miniaturized, and which does not impair the required characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a configuration example of a conventional digital processing type quadrature modulation device, FIG. 2 is a block diagram showing an example of a digital processing type quadrature modulation device according to the present invention, and FIG. FIG. 4 is a time chart explaining the operation of the device shown in the figure, and FIG. 4 is an explanatory diagram using a spectrum. 1-1, 1-2, 5-1, 5-2 are digital low-pass filters, 2-1, 2-2 are multiplication circuits,
3 is an adder circuit, 4 is a sine wave oscillator, 6 is a switching circuit, 7 is a digital-to-analog converter, and 8 is a bandpass filter.

Claims (1)

[Claims] 1. In a digital processing quadrature modulation device that amplitude-modulates a baseband signal using carrier waves orthogonal to each other and adds the amplitude, first and second signals are connected to the baseband signal and operate at different sample phases. Digital processing quadrature modulation characterized in that it is configured by sequentially connecting a digital low-pass filter, a circuit that time-divisionally scans and switches the outputs of both filters, a digital-to-analog converter, and a bandpass filter. Device.