JPH08102664A - Pll frequency synthesizer circuit - Google Patents

Abstract

PURPOSE: To prevent the generation of an excess amplitude level in a low frequency area and to reduce unnecessary radiation by obtaining a signal with a fixed amplitude level independently of the oscillation frequency of a VCO circuit from an amplifier circuit connected to the post stage of a VCO circuit. CONSTITUTION: The amplifier circuit 7 for amplifying the output signal from the VCO circuit 1 is constituted of a voltage/current conversion circuit 8 for inputting voltage VT to be impressed to the circuit 1 and converting the voltage VT into a current I2 proportional to the voltage value and a differential amplifier 9 for inputting the converted current I2 as an operation current. Or data corresponding to a frequency division number N are outputted from a controller for setting up the number N in a programmable devider and data obtained by DA converting the output data is impressed to the circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PLL frequency synthesizer circuit, and more particularly to an amplifier circuit connected to a VCO circuit.

[0002]

2. Description of the Related Art A PLL frequency synthesizer circuit includes a VCO circuit that outputs an oscillation frequency signal proportional to an applied voltage, a programmable divider that divides the output of the VCO circuit, a reference divider that divides a reference frequency signal,
P consisting of a phase comparator that compares the output phases of both dividers
It is composed of an LL circuit and a low-pass filter that inputs the output of the PLL circuit and applies a voltage to the VCO circuit.
Further, between the VCO circuit and the PLL circuit, in order to secure the input signal level to the PLL circuit at a predetermined level or higher,
Usually, an amplifier circuit is connected between the VCO circuit and the PLL circuit.

[0003]

However, in the amplifier circuit connected to the latter stage of the VCO circuit, the current amplification degree of the transistor in the output stage decreases as the frequency increases, so that the oscillation amplitude level output as a result is the frequency. Will be inversely proportional to. For example, as shown in FIG. 5, the output of the amplifier circuit in the FM radio receiver tends to decrease as the oscillation frequency increases.

Therefore, conventionally, the amplification degree of the amplifier circuit is generally set to be large so as to satisfy the minimum operation input level of the PLL circuit even when the frequency increases and the oscillation amplitude level decreases. However, in such a coping method, the oscillation amplitude level becomes excessive when the frequency is low, so that an unnecessary harmonic component is generated, which causes an increase in unnecessary radiation.

In recent years, there has been a particular demand for reduction of unnecessary radiation in radio receivers, and measures such as shortening the wiring of the VCO circuit and the PLL circuit have been taken as much as possible, but there is a limit to this, and based on the above cause. The generated unwanted radiation was a big problem.

[0006]

According to the present invention, there is provided a VCO circuit which outputs an oscillation frequency signal according to an applied voltage, a PLL circuit to which an output signal of the VCO circuit is input, and the PCO circuit.
In a PLL synthesizer circuit including a low-pass filter to which an output of the LL circuit is applied and which outputs an output voltage to the VCO circuit, amplification in which an amplification degree changes between the VCO circuit and the PLL circuit according to the oscillation frequency. The above problem is solved by inserting a circuit.

Further, the PLL frequency synthesizer circuit further has a controller for setting a frequency division number in a programmable divider included in the PLL circuit, and the controller stores data corresponding to the frequency division number to be set. The amplification circuit is configured to include a conversion circuit that outputs the data and converts the data into a voltage or a current, and an amplifier whose amplification degree changes according to the output from the conversion circuit.

Further, the amplifier circuit is characterized in that the voltage applied to the VCO circuit is input, and the amplification degree changes according to the input voltage. The amplifier circuit includes a voltage-current conversion circuit that converts a voltage applied to the VCO circuit into a proportional current, and a differential amplifier that inputs the current converted by the conversion circuit as an operating current. Characterize.

[0009]

When the amplification degree of the amplifier circuit after the VCO circuit is constant, the oscillation amplitude level decreases as the oscillation frequency increases, but in the present invention, the amplification degree increases accordingly as the frequency increases. Since it acts to increase the oscillation amplitude level, the oscillation amplitude level has a flat characteristic as a result, and the level reduction is prevented. Therefore, unlike the conventional case, it is not necessary to set the oscillation amplitude level as a whole high, the generation of an excessive amplitude level in the low frequency region is eliminated, and unnecessary radiation is reduced.

[0010]

1 is a block diagram showing a schematic configuration of an embodiment of the present invention, in which 1 is a VCO circuit which outputs an oscillation frequency signal proportional to an applied voltage, and 2 is an output f of the VCO circuit.
PLLLS including a programmable divider for dividing 0, a reference divider for dividing a reference frequency signal fr, and a phase comparator 5 for comparing output phases of both dividers.
I is a PLL circuit, 6 is a low-pass filter LPF that inputs the output of the PLL circuit 2 and applies the voltage VT to the VCO circuit 1, and 7 is inserted between the VCO circuit 1 and the PLL circuit 2, It is an amplifier circuit that amplifies the output signal of the circuit 1.

In this embodiment, the amplifier circuit 7 inputs the voltage VT applied to the VCO circuit 1 and converts the voltage VT into a current I2 proportional to the voltage value, and a converted current. It is composed of an amplifier 9 for inputting I2 as an operating current. Specific circuits of the voltage-current conversion circuit 8 and the amplifier 9 are shown in FIGS. 3 and 4, respectively. As shown in FIG. 3, the voltage-current conversion circuit 8 is a circuit that controls the operating current of the amplifier 9, and has transistors Q1 and Q1 having the same characteristics.
2 and a current mirror circuit composed of resistors, R2 and R3. Then, the applied voltage VT to the VCO circuit 1 is input to the collector of the transistor Q1 via the resistor R1. Therefore, the current I1 flowing through the transistor Q1 is proportional to VT / R1,
Moreover, since the currents I1 and I2 are equal to each other, the current I2 is also proportional to VT / R1. That is, the current I2 is
If the oscillation frequency f0 of the VCO circuit 1 becomes higher, it will increase accordingly.

The amplifier 9 has the differential amplifier configuration shown in FIG. 4, and the current I2 obtained by the voltage-current conversion circuit 8 is supplied as an operating current to both emitters of the transistors Q3 and Q4 constituting the differential amplifier. To be done. The oscillation signal from the VCO circuit 1 is input to the base of one transistor Q3, and the resistor R4 is connected to the base of the other transistor Q4.
Since the reference voltage from the dividing resistor of R5 is input, the amplification degree of this differential amplifier increases as the operating current I2 increases. Therefore, the higher the oscillation frequency f0, the higher the amplification degree of the differential amplifier 9.

Originally, when the operating current is constant, the amplitude level output from the differential amplifier 9 is as shown in FIG.
Although there is a characteristic that the higher the frequency is, the lower it is. However, in the amplifier of this embodiment, as shown in FIG. 6, conversely, the higher the oscillation frequency is, the higher the amplification is controlled. The decrease in the oscillation level shown in FIG. 5 is canceled by the increase in the amplification degree, and as a result, the oscillation amplitude level becomes the oscillation frequency as the overall characteristic as shown in FIG. 7 at the output stage of the amplifier circuit 7. It has a flat characteristic. Therefore, it suffices to set this flat constant value so as to satisfy the minimum operation level of the PLL circuit, and there is no fear of an excessive amplitude level even in the low frequency region, and generation of unnecessary radiation based on it is suppressed. .

Next, another embodiment of the present invention will be described with reference to FIG. The difference from the previous embodiment is that instead of using the voltage VT applied to the VCO circuit 1 as an input voltage of the voltage-current conversion circuit 8, a voltage based on the data output from the controller 10 is used. P
Normally, the pullable programmable divider 3 in the LL circuit 2 is
Controller 10 composed of microcomputer
The frequency division number N is set by the VCO circuit 1 and the frequency division number N is set.
It oscillates at the frequency corresponding to. Therefore, if the data DN corresponding to the frequency division number N to be set is output and the voltage DA-converted by the DA converter 11 is applied to the voltage-current conversion circuit 8, the amplification factor is set according to the oscillation frequency of the VCO circuit 1. Can be changed.

When controlling using such digital data, the amplification degree may be continuously changed according to the frequency as in the first embodiment, but the control is simplified. Therefore, the degree of amplification may be changed stepwise according to the oscillation frequency by using discrete data. Further, in the above description, an example is shown in which the amplification degree is increased in proportion to the oscillation frequency. However, if the original characteristic of the amplifier circuit is such that the amplitude level increases in proportion to the frequency, amplification is performed. The amplification factor of the circuit may be lowered in inverse proportion to the frequency.

[0016]

According to the present invention, a signal having a constant amplitude level can be obtained from the amplifier circuit connected to the subsequent stage of the VCO circuit regardless of the oscillation frequency of the VCO circuit. Therefore, in the low frequency region. A signal having an excessive amplitude level is not generated, and unnecessary radiation can be reduced.

[Brief description of drawings]

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

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

FIG. 3 is a specific circuit diagram of the voltage-current conversion circuit in the embodiment.

FIG. 4 is a specific circuit diagram of an amplifier according to an embodiment.

FIG. 5 is an output frequency characteristic diagram of a conventional amplifier circuit.

FIG. 6 is a frequency characteristic diagram of the amplification degree of the amplifier in the example.

FIG. 7 is an output total frequency characteristic diagram of the amplifier circuit in the example.

[Explanation of symbols]

 1 VCO circuit 2 PLL circuit 3 Programmable divider 6 LPF 7 Amplifying circuit 8 Voltage-current conversion circuit 9 Amplifier 10 Controller 11 DA conversion circuit

Claims (4)

[Claims] 1. A VCO circuit that outputs an oscillation frequency signal according to an applied voltage, a PLL circuit to which an output signal of the VCO circuit is input, and an output voltage to which the output of the PLL circuit is applied to output the VCO circuit. In a PLL frequency synthesizer circuit having a low-pass filter for outputting to a PLL, an amplifier circuit whose amplification degree changes according to the oscillation frequency is inserted between the VCO circuit and the PLL circuit. circuit. 2. The PLL frequency synthesizer circuit comprises:
Further, the programmable divider included in the PLL circuit has a controller for setting a frequency division number, the controller outputs data corresponding to the frequency division number to be set, and the amplifier circuit outputs the data as a voltage. Alternatively, the PLL frequency synthesizer circuit according to claim 1, comprising a conversion circuit for converting into a current and an amplifier whose amplification degree changes in accordance with an output from the conversion circuit. 3. The amplifier circuit according to claim 1, wherein the amplifier circuit is an amplifier circuit which inputs a voltage applied to the VCO circuit and whose amplification degree changes according to the input voltage.
LL frequency synthesizer circuit. 4. The amplifier circuit comprises a voltage-current conversion circuit that converts a voltage applied to the VCO circuit into a proportional current, and a differential amplifier that inputs the current converted by the conversion circuit as an operating current. The PLL frequency synthesizer circuit according to claim 3, wherein