JPS62166619A - Pll circuit - Google Patents

Abstract

PURPOSE:To prevent unnecessary radiation of a voltage controlled oscillator circuit, by selectively cutting off impression of supply voltages of those which do not correspond to a selected band of plural voltage controlled oscillator circuits by using a band switching signal, and so forth. CONSTITUTION:Outputs of voltage controlled oscillator circuits 7 and 7' are inputted to an analog amplifier 13 through capacitors 32 and 33 and the output of the amplifier 13 is led to a variable frequency dividing circuit 22. Since a transistor 28 is under a conducted state and another transistor 23 is set to a conducted state when a band switching signal S1 is high and another band switching signal S2 is low, and then, the 1st band is selected, a supply voltage is supplied to the voltage controlled oscillator circuit 7 and the circuit 7 makes oscillating operations. Moreover, transistors 29 and 24 and cut off since the band switching signal S2 is low and, accordingly, no supply voltage is applied across the voltage controlled oscillator circuit 7'. Therefore, the supply voltage controlled oscillator circuit 7' is set to a nonoperating state and unnecessary radiation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control means for a voltage controlled oscillator used in a channel selection device of a radio receiver or a television receiver, and in particular, it relates to a control means for a voltage controlled oscillator used in a channel selection device of a radio receiver or a television receiver. This invention relates to a PLL circuit used in a multiband synthesizer receiver configured with a synchronized loop.

2. Description of the Related Art FIG. 1 shows an example of a conventional synthesizer receiver in which a local oscillation circuit 6 is constituted by a PLL circuit.

This circuit captures broadcast radio waves from an antenna and uses RF
The mixer 3 extracts the frequency difference with the local oscillation circuit 6 through the amplification section 2, and the desired signal is obtained via the IF amplification section 4 and the detection circuit section 6.

Here, the local oscillation circuit 6 includes a reference oscillation circuit 11, a voltage controlled oscillation circuit 7, a variable frequency divider 9 whose output can be set to an arbitrary frequency division ratio, and an output of the variable frequency divider 9 and a reference oscillation circuit. Equipped with a phase comparator 10 for comparing the outputs of the circuit 11,
The output of the phase comparator 1o is applied to a voltage controlled oscillation circuit 7 via a low-pass filter 8 and controlled to obtain an output that oscillates at a predetermined frequency.

Since this variable frequency divider 9 performs digital signal processing,
The output of the voltage controlled oscillation circuit 7 must be amplified to a logic level by providing an amplifier.

Here, FIG. 2 shows a switching section of a conventional amplification circuit and a multiband voltage controlled oscillation circuit. The outputs of the voltage controlled oscillators 7, 7' are amplified by analog amplifiers 13, 14, and band switching signals S1. In S2, the signal is selected via the gate circuits 19, 20 and 21, and applied to the variable frequency dividing circuit section 22. Here, the band switching signal S1. The signal of S2 is sent to switching element 17.
18, the voltage controlled oscillation circuits 7 and 7' are operated so as to ground unnecessary outputs among the outputs, thereby reducing unnecessary radiation.

Problems to be Solved by the Invention As mentioned above, in the conventional example shown in FIG. 2, the unnecessary voltage controlled oscillation circuit output is grounded by the switching elements 17 and 18, thereby reducing unnecessary radiation. However, both voltage controlled oscillation circuits 7 and 7' are in an oscillating state, and are not configured to block unnecessary radiation emitted from them. Therefore, there has been a problem in that interference is often caused by unnecessary radiated signals.

Therefore, an object of the present invention is to provide a PLL circuit that prevents unnecessary radiation from the voltage controlled oscillation circuit.

Means to Solve the Problem In the present invention, the application of power supply voltages other than those corresponding to the selected band among the plurality of voltage controlled oscillation circuits is selectively cut off by using a band switching signal or the like. It was designed to do so.

Function By selectively cutting off and conducting the application of the power supply voltage of the voltage controlled oscillation circuit using a band switching signal etc. in this way, only the necessary voltage controlled oscillation circuit is operated and other unused voltages are turned off. Since the controlled oscillation circuit can be made inoperative, unnecessary radiation can be greatly reduced.

Embodiment Hereinafter, a PLL circuit according to an embodiment of the present invention will be explained with reference to the drawing of FIG.

The part corresponding to the variable division divider 9 in FIG. 1 is 12 in FIG.
2.33 to the analog amplifier 13, and its output is led to the variable frequency divider circuit 22.

Here, the voltage controlled oscillation circuits 7 and 7' are band switching circuits S
1. Switching circuits 30 and 31 are provided to cut off and conduct the application of the power supply voltage at S2. 23°24 is PNP
The transistor is pulled up through a resistor 24.25 and connected through a base resistor 26.27 to the collector of an NPN transistor 28.29. The emitters of the transistors 28, 29 are grounded, and the bases of each transistor 28, 29 are connected to band switching signals S1. S
2 is applied.

Here, when the first band is selected with the band switching signal S1 being -H1 and S2 being -L', the transistor 28 is in a conductive state, which causes the transistor 23 to be in a conductive state, so that the voltage A power supply voltage is supplied to the controlled oscillation (b) path 7, which operates in oscillation. Further, since the band switching signal S2 is 1L'', the transistor 29 is turned off, and the transistor 24 is also cut off, so that no power supply voltage is applied to the voltage controlled oscillation circuit 7'.

Therefore, the power supply voltage controlled oscillation circuit 7' becomes inoperative. This prevents unnecessary radiation.

Effects of the Invention As described above, according to the present invention, the PL
By cutting off and conducting the power supply voltage of the voltage controlled oscillation circuit for each band in the L circuit, it is possible to stop the oscillation of the oscillation circuit of unnecessary bands and reduce unnecessary radiation. It is possible to eliminate the need for complicated SWITCHing elements and selection gates as in the conventional example.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of the main part of a PLL circuit in an embodiment of the present invention, Fig. 2 is a block diagram showing the configuration of a general PLL synthesizer receiver, and Fig. 3 is a conventional circuit of the PLL section. FIG. 3 is a circuit diagram showing an example. 2...RF amplification section, 3...Mixer, 4
... IF amplification section, 6... detection circuit section,
6... Local oscillation circuit, 7.7'... Voltage controlled oscillation circuit, 8... Low pass filter,
9, 12...Variable frequency divider circuit, 1o...
Phase comparison circuit, 11...Reference frequency oscillation circuit,
30.31...Switching circuit for power supply voltage supply. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A plurality of voltage controlled oscillators corresponding to each band of the multi-band receiver, one analog amplifier to which the output of each voltage controlled oscillator is applied via a capacitor and amplifies the output, and a band selection among the voltage controlled oscillators. 1. A PLL circuit comprising switching means for applying a power supply voltage only to one voltage controlled oscillator to be selected in response to the PLL circuit.