JP3463388B2 - Quadrature detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature detection circuit,
In particular, the present invention relates to a quadrature detection circuit used in digital CATV. 2. Description of the Related Art In recent years, digital CAs have begun to spread rapidly.
The quadrature detection circuit used in the TV has a circuit configuration as shown in FIG. In the figure, 11 is CA
TV signal input terminal, 12 is CAT supplied to the input terminal
An amplifier 13 amplifies a signal supplied to the V input terminal and having a frequency of 5.5 to 750 MHz.
Mixer 14 connected to the output side of
An oscillator for generating a signal having a frequency of 1 MHz, the output of which is mixed with the output of the amplifier 13 by the mixer 13
It is converted into a signal that fluctuates around 1 MHz. Reference numeral 15 denotes a bandpass filter for filtering only a signal fluctuating around 961 MHz, 16 denotes a mixer connected to the output side of the bandpass filter 15, and 17 denotes a 916M
Oscillator for generating a signal with a frequency of Hz, 18 is 45 MH
a band-pass filter for filtering only the second intermediate frequency signal fluctuating around z; 19, a switch disposed on the output side of the band-pass filter 18; 20, an output terminal disposed on one output side of the switch 19; When the switch 19 is switched, a second intermediate frequency signal (analog signal) appears at the output terminal 20. Further, reference numeral 21 denotes a quadrature detector for extracting a digital output, and reference numeral 22 denotes a quadrature detector connected to the quadrature detector.
An oscillator for generating a signal having a frequency of 5 MHz, a terminal 23 connected to the output side of the quadrature detector 21 for extracting the in-phase signal (I), and a reference numeral 24 connected to the quadrature detector 21 to output the quadrature signal ( This is a terminal for taking out Q). [0005] In such a configuration,
Since two local oscillation oscillators and one local oscillation oscillator for quadrature detection are used to obtain the second intermediate frequency output, there is a limit in simplifying the circuit configuration. In addition, as the number of local oscillation oscillators increases, the spurious component also tends to increase. An object of the present invention is to solve such a problem. In order to solve such a problem, a local oscillation oscillator for performing quadrature detection and a second oscillator are provided.
The oscillator used for the intermediate frequency conversion is shared, in other words, the local oscillator circuit for quadrature detection and the second mixer are shared with the mixer for quadrature detection. If the local oscillation circuit for quadrature detection and the second mixer are used in common with the mixer for quadrature detection, the circuit configuration can be simplified as compared with the conventional one, and the number of oscillators can be reduced from three to two. Since the number of individual components can be reduced, spurious components can also be reduced. FIG. 1 shows a basic configuration of a quadrature detection circuit according to the present invention. In FIG. 1, the same components as those in FIG. 2 are denoted by the same reference numerals. In FIG. 2, the CATV signal terminal 11
The circuit configuration from to the bandpass filter 15 is the same as the conventional one. 31 is a divider connected to the output side of the bandpass filter 15, 32 and 33 are mixers respectively connected to the output side of the divider 31, and 34 is 961MH at the time of digital output.
z, an oscillator that generates a signal having a frequency of 916 MHz at the time of analog output. The oscillator 34 is directly connected to the mixer 33, and is connected to the mixer 32 via a π / 2 phase shifter 35. Reference numeral 36 denotes a low-pass filter connected to the output side of the mixer 32, 37 denotes a low-pass filter connected to the output side of the mixer 33, and 38 denotes a high-pass filter connected to the output side of the mixer 33. It is. Reference numeral 38 denotes a terminal connected to the output side of the low-pass filter 36 for extracting the in-phase signal (I), and reference numeral 39 denotes a terminal connected to the output side of the low-pass filter 37 for extracting the quadrature signal (Q). , 40 are terminals connected to the output side of the high-pass filter 38 to take out the second intermediate frequency output. With this configuration, the switching signal S is added to the selection of the oscillator 34 to switch the mode between digital output and analog output. At the time of digital output, the oscillator 34 converts the 961 MHz frequency signal into the mixer 33. , 32 directly or via a phase shifter 35, thereby sending an I signal to a terminal 38 and a Q signal to a terminal 39. That is, as a digital output, I / Q
To obtain an output, the outputs of the quadrature detection mixers 32 and 33 are connected to terminals 38 and 39 via low-pass filters 36 and 37.
Output the I / Q signal. At the time of analog output, the oscillator 34 outputs a 916 MHz frequency signal to the mixer 3.
3 and the frequency of 45 MHz
Is output as the second intermediate frequency output. As described above, if the quadrature detection circuit according to the present invention is used, the local oscillation circuit for quadrature detection and the second mixer share the mixer for quadrature detection. Since the circuit configuration can be simplified as compared with the conventional case and the number of oscillators can be reduced from three to two, spurious components can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a basic configuration of a quadrature detection circuit according to the present invention. FIG. 2 is a diagram illustrating a basic configuration of a conventional quadrature detection circuit. [Description of Signs] 11 CATV signal input terminal 12 Amplifiers 13, 16, 32, 33 Mixers 14, 17, 22, 34 Oscillator 15, 18 Bandpass filter 19 Switch 21 Quadrature detector 20, 23, 24, 38, 39, 40 terminal 35 phaser 36,37 low-pass filter 38 high-pass filter

Claims (1)

(57) [Claim 1] Means for converting a digital signal into a first intermediate frequency signal, a band-pass filter arranged on the output side of the means, and a band-pass filter arranged on the output side of the band-pass filter Distributor, first and second mixers arranged at the output side of the distributor, and first and second low-passes arranged at the output side of the first and second mixers An oscillator for selectively generating a signal having a different frequency from a filter, a high-pass filter connected to an output side of the second mixer, and an output terminal connected to an output side of each of the low-pass filter and the high-pass filter. Wherein the oscillator is directly connected to a second mixer and connected to the first mixer via a π / 2 phase shifter.