JP3393884B2 - Frequency synthesizer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer, and more particularly to a high frequency carrier switching frequency synthesizer used in a communication device.

[0002]

2. Description of the Related Art Conventionally, carrier switching time is several tens of μs.
When realizing a frequency synthesizer used for communication equipment of ec or less, it is difficult to realize with a general frequency synthesizer of one PLL circuit system. Therefore, as shown in FIG. 5, the two-system PLL circuits 1 and 2 are switched by the change-over switch 3 and output.

However, in the high frequency band, when the synthesizer having the above-mentioned configuration is used, the changeover switch 3 does not operate as an ideal changeover switch, and even when the changeover switch 3 is off, an input signal on one side leaks out and is output. I will end up.
This leak was a spurious of the synthesizer and was a performance defect. Specifically, the leakage of the changeover switch at 2 GHz is about -25 dB. FIG. 6 shows the isolation characteristic of the changeover switch 3. Figure 6
Shows the frequency on the horizontal axis and the insulation level on the vertical axis, indicating that the insulation level of the changeover switch 3 decreases as the frequency increases, and at high frequencies, the leakage of the signal passing through the changeover switch 3 occurs. You can see it grows.

[0004]

As described above, in the conventional frequency synthesizer, the changeover switch used for changing over the two PLL circuits has a lot of leakage when turned off in the high frequency band, which causes spurious at the output of the synthesizer. There was a problem.

Therefore, the present invention has been made in view of this problem, and it is a two-system PLL circuit and the two-system PLL circuit.
An object of the present invention is to provide a frequency synthesizer having a switch for selectively switching each output of the circuit, in which a leak is small when the changeover switch is off.

[0006]

In order to achieve the above object, the present invention provides a first PLL circuit, a second PLL circuit, an output of the first PLL circuit, and a second PLL circuit. A frequency synthesizer having a changeover switch for selectively changing between an output and a first buffer circuit connected between the first PLL circuit and the changeover switch, the second PLL circuit and the changeover switch. A second buffer circuit connected between the first buffer circuit and the second buffer circuit, a first power switch for supplying power to the first buffer circuit, and a second buffer circuit provided independently of the first power switch. A second power switch for supplying power to the circuit, and when the output of the first buffer circuit is selected by the changeover switch, the second power switch switches the second power switch to the second power switch. Turn off the buffer circuit,
When the output of the second buffer circuit is selected by the changeover switch, the power supply of the first buffer circuit is turned off by the first power supply switch. Here, each of the first buffer circuit and the second buffer circuit includes one or a plurality of buffer amplifiers. The first buffer circuit and the second buffer circuit each include a multiplier. Further, the first buffer circuit and the second buffer circuit are each composed of a combination of a buffer amplifier and a multiplier.

[0007]

In the frequency synthesizer of the present invention, the first
The first buffer circuit is connected between the PLL circuit and the changeover switch, and the second buffer circuit is connected between the second PLL circuit and the changeover switch, and the first buffer circuit and the second buffer circuit are connected. When the output of the first buffer circuit is selected by the changeover switch, a first power supply switch and a second power supply switch for independently supplying power to the buffer circuit are provided. When the output of the second buffer circuit is selected by the changeover switch and the power supply of the second buffer circuit is turned off, the power supply of the first buffer circuit is turned off by the first power supply switch. With such a configuration, the first buffer circuit and the second buffer circuit can be completely separated in both the power supply circuit and the control circuit, whereby the second PLL circuit at the time of switching the switches can be separated. The leakage of the output to the output of the first PLL circuit and the leakage of the output of the first PLL circuit to the output of the second PLL circuit can be effectively reduced.

[0008]

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

In FIG. 1, 1 and 2 are PLL circuits, 3 is a changeover switch, and 4 and 5 are buffer circuits of the PLL circuits 1 and 2. Further, 10 and 12 are buffer circuits 4 and 5.
, 11 and 13 are power switches of the power sources 10 and 12.

The PLL circuit 1 and the PLL circuit 2 are always on and set to different carrier frequencies.
Numerals 4 and 5 are buffer circuits, which are composed of, for example, buffer amplifiers. The buffer circuits 4 and 5 can be turned on and off independently of the PLL circuits 1 and 2 and the changeover switch 3.

In the frequency synthesizer shown in FIG.
When outputting the L circuit 1 side, first, the power switch 11 is turned on to turn on the power supply 10 of the buffer circuit 4, and the power switch 13 is turned off to turn off the power supply 12 of the buffer circuit 5. As a result, the PLL circuit 2 not used
The leakage of the output of is significantly reduced by the buffer circuit 5. Next, the changeover switch 3 is switched to the PLL circuit 1 side. As a result, the output of the PLL circuit 1 side becomes the synthesizer output. At this time, the output of the PLL circuit 2 side is the isolation when the power supply of the buffer circuit 5 is off and the changeover switch 3
The leakage is only the combined amount of isolation. Therefore, the leakage of the output on the PLL circuit 2 side is considerably reduced,
Spurious as a frequency synthesizer can also be reduced.

Next, other embodiments of the frequency synthesizer of the present invention are shown in FIGS. 2, 3 and 4, respectively.

Although the power supply and the power supply switch are not shown for convenience in the frequency synthesizers of FIGS. 2, 3 and 4, they will be described below as being present.

FIG. 2 shows the buffer circuits 6 and 5 in the buffer circuits 4 and 5 in the frequency synthesizer shown in FIG.
7 is added to form a two-stage configuration, so that signal leakage can be further reduced.

FIG. 3 is a circuit in which multiplication circuits 8 and 9 having a buffer function are provided after the PLL circuits 1 and 2, and the output frequency of the frequency synthesizer is N times that of PLL1 and PLL2. In this case, PL
It is the same that the leakage of the signal on one side that does not use the outputs of the L circuits 1 and 2 is reduced, but since the multiplier circuits 8 and 9 are provided, the isolation of the buffer circuits 4 and 5 when the power is off is more improved. It is large and the signal leakage is small.

FIG. 4 is a circuit in which buffer circuits 4 and 5 are provided before the frequency multiplying circuits 8 and 9 in the frequency synthesizer shown in FIG. 3 to further reduce signal leakage.

As described above, according to this embodiment, it is possible to realize a frequency synthesizer capable of high-speed carrier switching and good spurious performance.

Further, at present, the digitalization is progressing also in the mobile communication system, and particularly in the case of the time division multiplexing system, it is necessary to switch the transmission and reception at high speed, and even when the frequency synthesizer used for this is realized. Easily available.

[0019]

As described above, in the frequency synthesizer of the present invention, the buffer circuit is provided between the two PLL circuits and the changeover switch, and the power supply of this buffer circuit is turned on and off, whereby the changeover switch is turned off. The leakage can be made smaller and the spurious performance of the synthesizer is not significantly deteriorated.

Therefore, it is possible to realize a frequency synthesizer capable of high-speed carrier switching and good spurious performance.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing another embodiment of the frequency synthesizer of the present invention.

FIG. 3 is a block diagram showing another embodiment of the frequency synthesizer of the present invention.

FIG. 4 is a block diagram showing another embodiment of the frequency synthesizer of the present invention.

FIG. 5 is a block diagram of a conventional frequency synthesizer.

FIG. 6 is a diagram showing isolation (insulation) characteristics.

[Explanation of symbols]

1 PLL circuit 2 PLL circuit 3 Changeover switch 4 buffer circuit 5 buffer circuit 6 buffer circuit 7 Buffer circuit 8 multiplication circuit 9 multiplication circuit 10 power supplies 11 Power switch 12 power supplies 13 Power switch

   ─────────────────────────────────────────────────── ─── Continued front page       (56) Reference JP-A-1-314435 (JP, A)                 JP-A-4-160908 (JP, A)                 Actual Kaihei 3-120133 (JP, U)

Claims (4)

(57) [Claims] 1. A frequency synthesizer having a first PLL circuit, a second PLL circuit, and a changeover switch for selectively switching the output of the first PLL circuit and the output of the second PLL circuit. A first buffer circuit connected between the first PLL circuit and the changeover switch, a second buffer circuit connected between the second PLL circuit and the changeover switch, A first power switch that supplies power to the first buffer circuit; and a second power switch that is provided independently of the first power switch and that supplies power to the second buffer circuit. When the output of the first buffer circuit is selected by the changeover switch, the power supply of the second buffer circuit is turned off by the second power supply switch, and the changeover switch is turned on. Wherein when the output has been selected a second buffer circuit, a frequency synthesizer, characterized in that to turn off the power source of the first buffer circuit by the first power supply switch by. 2. The first buffer circuit and the second buffer circuit
2. The frequency synthesizer according to claim 1, wherein each of the buffer circuits comprises one or a plurality of buffer amplifiers. 3. The first buffer circuit and the second buffer circuit
2. The frequency synthesizer according to claim 1, wherein each of the buffer circuits comprises a multiplier. 4. The first buffer circuit and the second buffer circuit
2. The frequency synthesizer according to claim 1, wherein each of the buffer circuits comprises a combination of a buffer amplifier and a multiplier.