JPH06253226A - Receiver in common use for digital and analog signal - Google Patents

Abstract

PURPOSE:To provide an inexpensive system with simple configuration having lots of common use parts while receiving both an analog modulation signal and a digital modulation signal. CONSTITUTION:An input signal is up-converted by an oscillation output from a 1st local oscillator 12 at a 1st frequency converter 11 and fed to a distributer 14 as a 1st intermediate frequency signal. Phase detectors 15, 16 are connected to two output terminals of the distributer 14 and oscillation outputs from a voltage controlled oscillator 21 are received respectively with a phase difference of 90 deg.. Phase synchronization is executed with a predetermined frequency by a PLL circuit. When an analog modulation signal is inputted, the phase detector 15 acts as a mixer and 2nd frequency conversion is realized to obtain a 2nd intermediate frequency (down-convert signal). Moreover, when a digital modulation signal is inputted, outputs of the phase detectors 15, 16 are I axis demodulation component and Q axis demodulation component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital / analog shared receiver which is effective when digital image transmission is introduced in satellite broadcasting or cable television (CATV) transmission and is transmitted together with conventional analog transmission. Regarding

[0002]

2. Description of the Related Art In a conventional receiving system, an analog receiving device and a digital receiving device are independent.

FIG. 2A shows a cable television (CA).
2 shows a double super tuner receiving a signal by (TV) transmission. Input frequency (RF) (frequency 50 to 10
00 MHz) is mixed with the local oscillator from the first local oscillator 82 in the first frequency converter 81, converted into a first intermediate frequency signal higher than the upper limit of the input frequency, and the first band pass filter. 2 through 8 a frequency converter 8
Introduced in 4. The first intermediate frequency signal is mixed in the second frequency converter 84 with the local oscillation output from the second local oscillator 85 and is again converted into the second intermediate frequency signal of the second band pass filter 86. Taken out through. In this example, the input frequency is 50 MHz to 1 GHz, the first intermediate frequency is 1.2 GHz, and the second intermediate frequency is 4 GHz.
It is set to 5.75 MHz. The signal of the second intermediate frequency is input to the detection circuit connected to the subsequent stage and demodulated.

FIG. 2B shows an example of a demodulation circuit for a 16QAM modulated signal transmitted by digital transmission. The signal received by the tuner 90 and converted into the intermediate frequency is supplied to the phase detectors 92 and 93 via the bandpass filter 91. The phase detectors 92 and 93 are supplied with the carrier from the local oscillator 94, and are directly supplied to the phase detector 92 and to the phase detector 93 via the π / 2 phase shifter 95. . As a result, the phase detectors 92, 93
Quadrature detection components are obtained from the respective components, and the respective components are quaternary-to-binary converters 96a, 9 as a data reproducing unit.
6b. The four-value / two-value converters 96a and 96b respectively convert the four-valued AM signal into two series of binary pulses and output them as reproduction data Q and I.

The outputs of the phase detectors 96a and 96b are supplied to a clock synchronization circuit 97 and a carrier wave recovery circuit 98. The carrier recovery circuit 98 detects an error signal from the difference between the detected phase of the symbol and the specific phase information, and supplies this to the oscillation frequency control terminal of the local oscillator 94. The clock synchronization circuit 97 creates an internal clock in synchronization with the input symbol phase, and the 4-value / binary converter 96
It is supplied to a and 96b for data reproduction.

[0006]

As described above, in the past, there is almost no case where analog and digital transmissions are mixed in the same transmission medium. But recently,
Due to the progress of digital image compression technology, it is conceivable to perform digital image transmission in addition to analog transmission as a method of increasing the number of channels in CATV. However, because the existing system is an analog transmission and reception system,
Problems occur on the receiving side.

Therefore, an object of the present invention is to provide an analog / digital receiving device which can receive both analog modulated signals and digital modulated signals and can increase the number of common parts.

[0008]

The present invention provides a first intermediate frequency signal frequency-converted to a high frequency by multiplying an input signal by a local oscillation output from a first local oscillation means. A frequency converter, a first bandpass filter for deriving the first intermediate frequency from the first frequency converter, and outputs of the first bandpass filter to first and second output sections. A distributor for distributing to the first, and the first
The first and second phase detectors respectively connected to the output section and the second output section of the second phase pass filter, and a second bandpass filter for deriving a second intermediate frequency from the output of the first phase detector or A switch for selectively deriving to a first quadrature detection component deriving terminal, and a second quadrature generated by using a phase-locked loop in which each of the first and second phase detectors has a predetermined phase difference. The second local oscillation means for supplying the local oscillation output of

[0009]

When the digital modulation signal is input by the above means, the quadrature detection or the quasi-coherent detection is realized by the first and second phase detectors and the second local oscillating means to obtain the Q axis component and the I axis component. You can When receiving the analog modulation signal, the first frequency converter can obtain up-conversion, and the next first phase detector can obtain down-conversion to convert to the second intermediate frequency.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. A high frequency signal is introduced into the input terminal 10 and supplied to the first frequency converter 12. In this first frequency converter 11,
The local oscillation output from the first local oscillator 12 is supplied. This multiplies the input signal by the local oscillator output,
The input signal becomes a first intermediate frequency signal that has been frequency-converted (up-converted) to a high frequency. The first intermediate frequency signal is supplied to the distributor 14 after the unnecessary components are removed by the first band-pass filter 13 and derived.

The distributor 14 distributes the input signal to the first and second outputs. The signal of the first output section is supplied to the first phase detector 15, and the signal of the second output section is supplied to the second phase detector 16. The output of the first phase detector 15 is supplied to the input end of a switch 17, and the switch 17 guides the input signal to a bandpass filter 18 or an output terminal 19. The output of the second phase detector 16 is led to the output terminal 20.

The first and second phase detectors 15 and 16 are supplied with a second local oscillation output generated by using a phase locked loop with a phase difference of 90 °. ing. That is, the output of the voltage controlled oscillator 21 is directly supplied to the first phase detector 15 and is supplied to the second phase detector 16 via the 90 ° phase shifter 22. The output of the voltage controlled oscillator 21 is introduced into the phase locked loop circuit (PLL circuit) 25. PLL
The circuit 25 compares the oscillation output of the voltage controlled oscillator 21 and the fixed oscillation output of the fixed local oscillator 27 in phase, detects an error between them, smoothes them by the low-pass filter 26, and performs voltage control using this smoothed output as a control signal. It is supplied to the frequency and phase control end of the oscillator 21.

In the above embodiment, it is assumed that a digital modulation signal is being input now. In this case switch 1
7 outputs the output of the phase detector 15 to the output terminal 19 as an I-axis component. The high frequency signal is the first frequency converter 1
Up-converted by 1 and sent to the quadrature detection unit. That is, quadrature detection or quasi-synchronous detection is executed by the phase detectors 15 and 16, and an I-axis demodulation component is obtained at the output end 19 and a Q-axis demodulation component is obtained at the output terminal 20. If the fixed local oscillator 27 is fixed oscillation, quasi-synchronous quadrature detection is performed, and if it is a voltage control type or a numerical control type, synchronous detection is performed.

Next, when the analog modulation signal is input, it is up-converted in the first frequency converter 11, and the first phase detector 15 multiplies (mixes) the first intermediate frequency signal and the local oscillation output. ) Is performed, and conversion (down conversion) into a second intermediate frequency signal is realized as an output. At this time, the switch 17 sends the second intermediate frequency signal from the phase detector 15 to the band pass filter 1
Introduce to 8.

That is, the above circuit operates as a single super IQ demodulator during digital reception. The frequency of the first intermediate frequency signal at this time is substantially equal to the oscillation output frequency of the oscillator 21. Therefore, the I-axis component and the Q-axis component are almost baseband signals. Also,
The phase detectors 15 and 16 are composed of complex multipliers.
After this demodulation, analog-to-digital conversion is performed and data reproduction is performed. Next, during analog reception, it operates as a double super tuner. At this time, the frequency 2ndIF of the second intermediate frequency signal and the frequency 1st of the first intermediate frequency signal
The relationship between the IF and the oscillation output frequency 2ndLO of the oscillator 21 is such that 2ndIF = 1stIF-2ndLO.

The present invention is not limited to the above embodiment. It may be configured as shown in FIG. The same parts as those in the previous embodiment are designated by the same reference numerals, and different parts will be described. That is, the I-axis demodulation component and the Q-axis demodulation component of the output terminals 19 and 20 are introduced into the carrier wave reproduction loop circuit 31.

The carrier recovery loop circuit 31 is adapted to obtain an error signal between the symbol phase and a predetermined phase using the I-axis and Q-axis demodulation components. For example, the I-axis demodulation component and the Q-axis demodulation component are digitally converted and input to the complex multiplier. In the complex multiplier, for example, the oscillation data from the numerically controlled oscillator is converted into data of cos characteristic and sin characteristic, and I-axis component and Q-axis component are respectively subjected to complex operation,
The real part data and the imaginary part data are obtained. This data is supplied to the phase comparator. The phase comparator outputs the amount of deviation of the phase represented by the real part data and the imaginary part data from a predetermined phase (for example, the symbol phase), that is, a phase error. The numerically controlled oscillator is controlled by this phase error so that the symbol phase and the oscillation phase are synchronized. Since the phase error information obtained in the process of this control also indicates the synchronization shift in the quadrature detection unit, for example, this shift information is used for the frequency control (AF) of the voltage controlled oscillator 21.
It can be used for C). Therefore, at the time of digital reception, the switch 32 is switched so as to introduce the output of the carrier recovery loop circuit 31 into the voltage controlled oscillator 21, and at the time of analog reception, the low pass filter 26 of the low pass filter 26 is used as in the previous embodiment. The output is supplied to the control terminal of the voltage controlled oscillator 21.

As described above, this system is applied to the digital demodulation device by using the switch 18 and the band pass filter 1.
By providing 8, the phase detector 15 can be utilized as a mixer for analog reception. Conversely speaking, for the up-down converter using the phase comparator 15 as the second frequency converter, the phase comparators 16 and 9 are used.
By providing the 0 ° phase shifter 22, it can be easily utilized as a digital demodulator.

Further, in the present invention, the first local oscillator 12 is a voltage control type oscillator, and at the time of analog reception, the output of the carrier recovery loop circuit is fed back to the oscillator of the first frequency conversion unit as an AFC control voltage. You may use it.

[0021]

As described above, according to the present invention,
This is effective for realizing an inexpensive system that allows reception of both analog modulated signals and digital modulated signals and has many common parts.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional analog receiver and digital receiver.

[Explanation of symbols]

11 ... 1st frequency converter, 12 ... 1st local oscillator,
13 ... Band pass filter, 14 ... Distributor, 15, 16 ...
Phase detector, 17 ... Switch, 18 ... Band pass filter, 21 ... Voltage controlled oscillator, 25 ... PLL circuit, 26 ...
Low-pass filter, 27 ... Fixed oscillator.

Claims (1)

[Claims] 1. A first frequency converter for obtaining a first intermediate frequency signal frequency-converted to a high frequency band by multiplying a local oscillation output from a first local oscillation means and an input signal; A first bandpass filter for deriving the first intermediate frequency from a first frequency converter; a distributor for distributing the output of the first bandpass filter to first and second output sections; First and second phase detectors respectively connected to the first output section and the second output section, and a second band pass for deriving a second intermediate frequency from the output of the first phase detector It is generated by using a filter or a switch for selectively deriving to the first quadrature detection component deriving terminal and a phase-locked loop with the first and second phase detectors having a predetermined phase difference from each other. A second local oscillator output providing a second Digital analog common receiving apparatus characterized by comprising a part oscillating means.