JPH114201A - Fm modulation wave transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide FM modulation wave output without output deviation owing to the change of a carrier frequency. SOLUTION: In FM modulation wave transmission by an FM modulator 3, a base band part oscillates a test signal on the plural carrier frequencies F which are scheduled. An output measuring part 4 monitors the output of the FM modulator 3, measures a normalized transmission amplification factor a(F) and stores an obtained control table in an adjusting value storage part 5. At the time of starting transmission of an FM modulation wave, a control part 1 reads the normalization transmission amplification factor a(Fn) corresponding to the transmission carrier frequency Fn and sets the amplification factor of a base band correction part 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an FM modulated wave transmitter used for frequency multiplex communication.

[0002]

2. Description of the Related Art In recent information communication networks, signal multiplexing has been advanced. In a multiplexed network,
A large number of signals are regularly grouped so as not to interfere with each other and are transmitted through one transmission line. There are various types of multiplexing. One of them is a frequency division multiplex system. In the frequency division multiplexing method, a plurality of carriers having different frequencies are modulated with a plurality of signals to be transmitted, and transmitted. One of the modulation methods is an FM modulation method. The FM modulation method has been adopted in many fields because of its resistance to noise and the like.

[0003] In this FM modulation method, an FM modulated wave transmitter is indispensable. Generally, a VCO using a variable capacitance diode is used for an FM modulated wave transmitter. The VCO is an oscillator that changes the capacitance by applying a DC reverse bias to the variable capacitance diode to change the oscillation frequency.
Hereinafter, this DC reverse bias is referred to as a control voltage. Conventional FM
In the modulated wave transmitter, a constant control voltage is applied to the VCO to oscillate. The oscillation wave at that time is defined as a carrier wave. Furthermore, FM modulation is performed by directly changing the control voltage according to the amplitude of a signal to be transmitted.

[0004]

However, the conventional FM modulated wave transmitter as described above has the following problems to be solved. When an FM-modulated wave transmitter FM-modulates a carrier with a signal to be transmitted and transmits the signal, the receiver performs FM detection on the signal to extract a signal to be transmitted. At this time, even if the amplitude of the signal to be transmitted is the same, if the frequency of the carrier is different, there is a problem that the amplitude of the signal to be transmitted extracted by the FM detection and extracted by the receiver has a deviation.

[0005]

The present invention adopts the following constitution in order to solve the above points. <Configuration> A baseband unit that oscillates a test signal for measuring the characteristics of the device, a baseband correction unit that increases and decreases the amplitude of the test signal output from the baseband unit, and a test signal output from the baseband correction unit For any carrier frequency at which FM modulated wave transmission is scheduled
An FM modulator that obtains a modulated wave output, an output measuring unit that detects the FM modulated wave output output from the FM modulator, and measures the amplitude of the detected output, based on a measurement result of the output measuring unit, An adjustment value storage unit that stores the amplitude ratio of the detection output with respect to the amplitude of the test signal as control data in association with each carrier frequency at which FM modulated wave transmission is scheduled; and any one of the plurality of carrier frequencies. When selecting a carrier frequency and causing the FM modulator to transmit an FM modulated wave, the control signal stored in the adjustment value storage unit is referred to, and the input signal is determined by the amplitude ratio of the detection output to the amplitude of the corresponding test signal. An FM modulated wave transmitter, comprising: a control unit for operating the baseband correction unit so as to increase or decrease.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below using specific examples. FIG. 1 is a block diagram of an FM modulated wave transmitter according to the present invention. Before describing the FM modulated wave transmitter shown in FIG. 1, the configuration of the FM modulator 3 which plays a central role in the FM modulated wave transmitter in FIG. 1 will be described with reference to FIG.

<Configuration of FM Modulator> FIG. 2 is an explanatory diagram of the FM modulator 3. (A) is a block diagram of a basic configuration. (B) is a circuit example of a resonance circuit. (C)
5 is a characteristic example of a variable capacitance diode used in a resonance circuit.
1A, the FM modulator 3 includes a resonance circuit 10, an amplification circuit 11, and a feedback circuit 12.

The resonance circuit 10 is a circuit for determining the carrier frequency F of the FM modulator 3. The circuit includes an inductance L and a capacitance C1, as shown in FIG.
C2, Cs, and variable capacitance C by variable capacitance diode
v. Here, Cs is the sum of all stray capacitances in the circuit. The resonance frequency at this time is
(1) It can be expressed by the equation (in the figure). (1) where f (Cv) is
It represents the total capacitance in the circuit, and indicates that this value depends on the change in the variable capacitance Cv due to the variable capacitance diode. A variable capacitance diode is a type of semiconductor diode having a PN junction.

When a DC reverse bias is applied to the PN junction,
A layer lacking carriers (electrons and holes) is formed at the PN junction. This is called a depletion layer. This depletion layer functions as a capacitance. The magnitude of this capacitance is P
It changes depending on the magnitude of the DC reverse bias applied to the N junction. An example of the change is shown in FIG. The horizontal axis shows the magnitude Vc of the DC reverse bias applied to the PN junction, and the vertical axis shows the capacitance Cv at that time. It should be noted here that the curve representing the variable capacitance Cv is far from the straight line. Therefore, it is naturally expected that the expression (1) representing the resonance frequency F of the resonance circuit shown in (b) does not become a simple straight line.

The amplifying circuit 11 is a circuit that receives a part of the resonance current from the resonance circuit 10 and amplifies it. Generally, the FM modulator 3 used for the FM modulated wave transmitter or the like is required to output a plurality of carrier frequencies. It is desirable that the level deviation between the plurality of carrier frequency outputs be small. In order to satisfy this requirement, the amplifier circuit 11 is configured by a wideband amplifier having a flat amplification factor from a low cutoff frequency to a high cutoff frequency. The feedback circuit 12 returns a part of the output of the amplifier circuit 11 to the resonance circuit 10, and performs the amplification circuit 11, the feedback circuit 12, the resonance circuit 10, the amplification circuit 11
And a circuit forming a positive feedback loop.

<Operation of FM Modulator> The FM modulator 3 described above operates as follows. When the control voltage Vc1 is applied to the control voltage input terminal Tc in FIG. 2A, the variable capacitance Cv of the variable capacitance diode is changed according to the control voltage Vc1.
(FIG. 2B) changes to Cv1. This Cv1 determines the resonance frequency F1 of the resonance circuit 10 at that time according to the equation (1). An output using F1 as the carrier frequency is output from the FM modulated wave output terminal To of the FM modulator 3.

Similarly, when the control voltage Vc2 is applied to the control voltage input terminal Tc, the variable capacitance Cv of the variable capacitance diode changes to Cv2 according to the control voltage Vc2. From this Cv2, the resonance frequency F2 of the resonance circuit 10 at that time is determined according to the equation (1). The output using F2 as the carrier frequency is the FM modulated wave output terminal T of the FM modulator 3.
Output from o. Hereinafter, the carrier frequency F is measured while the control voltage Vc is successively changed, and the results are shown in the figure, with the control voltage Vc on the horizontal axis and the carrier frequency F on the vertical axis, to obtain FIG.

FIG. 3 is a diagram showing the relationship between the control voltage Vc of the FM modulator and the carrier frequency F. As shown at points (A) and (B) in FIG. 3, the slope of this curve is not constant at each point on the curve. The effect of the fact that the slope of the curve is not constant at each point on the curve, which affects the characteristics of the FM modulator 3 will be described below. It is assumed that the control voltage Vc is changed by ΔV at a point (A) on the drawing. The change in the carrier frequency F at that time is ΔF1 around F1. Similarly, the control voltage Vc is changed at the point (B) in the drawing by Δ
It is assumed that V is changed. The change in the carrier frequency F at that time is ΔF2 centered on F2. In the figure, (A)
A deviation occurs between the variation ΔF1 of the carrier frequency F at the point and the variation ΔF2 of the carrier frequency F at the point (B).

Here, the reason why the control voltage Vc is changed by ΔV around the points (A) and (B) is that the signal having the amplitude ΔV / 2 is input to the modulation wave input terminal Tm in FIG. Nothing else. Hereinafter, this signal is referred to as a modulated wave. Therefore, Δ
The reason why the deviation occurs between F1 and ΔF2 is that it is not preferable that even if the modulation is performed by the same modulation wave, if the carrier frequency F at that time is different, a deviation occurs in the modulation rate. Therefore, the FM modulated wave transmitter according to the present invention has a configuration as shown in FIG. 1 in order to reduce this frequency deviation. Returning to FIG. 1, the specific configuration and features of the FM modulated wave transmitter according to the present invention will be described.

<Configuration of FM Modulated Wave Transmitter> Referring to FIG. 1, an FM modulated wave transmitter according to the present invention includes a control unit 1, a baseband correction unit 2, an FM modulator 3, and an output measuring unit 4.
And an adjustment value storage unit 5 and a baseband unit 6. The control unit 1 is a unit that applies a control voltage to a control voltage input terminal Tc provided in the FM modulator 3 to change the variable capacitance Cv of the variable capacitance diode, thereby changing the carrier frequency F. Hereinafter, the control voltage applied to the control voltage input terminal Tc is referred to as a frequency control voltage. Further, it is a portion that applies a control signal to the baseband correction unit 2 and controls an increase or decrease in the amplitude of the modulated wave input to the modulated wave input terminal Tm provided in the FM modulator 3. Hereinafter, the control signal applied to the baseband correction unit 2 is referred to as an amplitude control voltage. At the same time, it is a part for writing and reading a measurement result (described later) on the modulated wave transmitted from the measuring device controller 8 to the adjustment value storage unit 5. Further, the test signal S is supplied to the baseband unit 6.
It is also the part that requests t.

The baseband correction unit 2 receives a modulated wave from the baseband unit 6. At the same time, an amplitude control voltage is input from the control unit 1. The amplitude of the modulated wave is increased or decreased by the amplitude control voltage. This is a section for applying the modulated wave whose amplitude has been increased or decreased to the modulated wave input terminal Tm provided in the FM modulator 3 to change the variable capacitance Cv by the variable capacitance diode. FM
The modulator 3 includes the resonance circuit 10, the amplification circuit 11, and the feedback circuit 12, as described in detail with reference to FIG. The control unit 1 controls the control voltage input terminal T
The carrier is oscillated by the frequency control voltage applied to c. Further, the modulated wave whose amplitude has been increased / decreased is applied to the modulated wave input terminal Tm by the baseband correction unit 2, and the carrier wave is
Perform M modulation. This section outputs the FM modulated wave output Fout to the FM modulated wave output terminal To.

The output measuring section 4 monitors the FM modulated wave output Fout of the FM modulator 3 and outputs the FM modulated wave output Fou.
From t, the frequency of the carrier and the amplitude of the modulated wave are measured. This is a part for transmitting the result to the control unit 1, and is composed of an FM detector 7 and a measuring device controller 8. F
The M detector 7 is a part that inputs a part of the FM modulation wave output Fout from the FM modulation wave output terminal To provided in the FM modulator 3 and performs FM detection to extract a modulation wave. For the FM detection, a frequency discriminator that changes a change in the frequency F of the FM modulated wave output Fout into a change in voltage is used. Usually, the slope of the resonance curve is used for the frequency discriminator.

FIG. 4 is an explanatory diagram of a frequency discriminator using a resonance curve. The horizontal axis represents the change in the frequency F of the FM modulated wave output Fout, and the vertical axis represents the amplitude v. (A) shows the case of one resonance circuit. When the frequency is changed by ΔF around the frequency F1 at the point A on the curve, the amplitude change becomes Δv1. Similarly, when the frequency is changed by ΔF around the frequency F2 at the point B on the curve, the amplitude change becomes Δv2. Δv
A large deviation occurs between 1 and Δv2. This is due to the linearity of the resonance curve. In (b), the resonance circuit is 2
The difference of the output is taken out using this. It can be understood that a frequency discriminator having good linearity as shown by a broken line is obtained. As described above, it is common to use two resonance circuits as the frequency discriminator. The measuring device controller 8 is a portion that extracts the amplitude Vd of the FM detection output and the frequency F of the carrier wave at that time from the FM detector 7 and transmits the result to the control unit 1.

The adjustment value storage section 5 is a section in which the control section 1 writes and reads out the results extracted by the measuring instrument controller 8. The baseband unit 6 includes an input signal,
For example, an audio signal or a video signal is converted into an electric signal. The converted electric signal is output to the baseband correction unit 2 as a modulated wave. In addition, it is a portion that oscillates the test signal St and outputs it to the baseband correction unit 2 at the request of the control unit 1. The test signal St refers to, for example, a sine wave having a constant frequency and a constant amplitude.

<Operation of FM Modulated Wave Transmitter> The operation of the FM modulated wave transmitter described above will be described. First, the characteristics of the FM modulated wave transmitter will be described with reference to FIG. FIG.
FIG. 4 is a relationship diagram between a frequency control voltage change and an FM detection output. FIG. 5A shows the frequency control voltage Vc on the horizontal axis,
The vertical axis indicates the carrier frequency F. The test signal St is shown at the bottom of the figure.
Is shown. This figure shows the FM modulator 3 already described.
(FIG. 1), which is the frequency control voltage Vc0.
A large deviation occurs in the amount of change ΔF in the carrier frequency F between the case where ΔVc is changed around the center and the case where ΔVc is changed around the frequency control voltage Vcn.

FIG. 5B shows the FM detection output Vd on the horizontal axis, the carrier frequency F on the vertical axis, and FIG.
To match. In the upper part of the figure, the FM detection outputs D0, D
n and Dm. This (b) shows the characteristics of the FM detector 7, which correlates with the characteristics of the frequency discriminator already described (FIG. 4 (b)), and is almost a straight line. Accordingly, the variation ΔF of the carrier frequency F in (a) is directly reflected on the variation ΔVd of the FM detection output Vd.

The FM modulated wave transmitter according to the present invention performs the following measurements before starting transmission to the network. FIG. 5 (a) shows a test signal St shown in the lower part of FIG.
When M modulation is performed, the FM detection output D shown in the upper diagram of FIG.
Measure how the amplitudes of 0, Dn, Dm change with carrier frequency F. This value is referred to as the transmission amplification factor A.
(F) is defined. 5A and FIG.
(F) = ΔVd / ΔVc. The measurement of the transmission amplification factor A (Fn) will be described with reference to FIG. In FIG. 1, the control unit 1 changes the frequency control voltage Vc0 (FIG. 5A) to F
The voltage is applied to the control voltage input terminal Tc of the M modulator 3. At the same time, a test signal St is requested to the baseband unit 6. This test signal St is a sine wave having an amplitude ΔVc / 2.

The FM modulator 3 to which the frequency control voltage Vc0 (FIG. 5A) is applied receives the carrier frequency F0 (FIG. 5A).
(A) The carrier wave is oscillated. This operation is shown in FIG.
At the point P0. At the same time, the baseband unit 6
The test signal St is oscillated at the request of the control unit 1. This test signal St is applied to the modulation wave input terminal Tm of the FM modulator 3 via the baseband correction unit 2, and changes the frequency control voltage V0 with a sine wave having an amplitude ΔVc / 2. Here, it is assumed that the amplification factor of the baseband correction unit 2 is 1.
This state is equivalent to FM modulation of the carrier frequency F0 (FIG. 5A) with the test signal St (lower part of FIG. 5A). As a result, the FM modulator 3 outputs the FM carrier output terminal T0.
Outputs an FM modulated wave output Fout which shifts by ΔF0 around the carrier frequency F0.

The FM detector 7 outputs the FM modulated wave output Fo.
ut is detected to obtain an FM detection output D0 (above (b)). From the D0, the measuring instrument controller 8 calculates Δ
Vd0 (above (b)) is measured. The value of ΔVd0 and the carrier frequency F0 at that time are sent to the control unit 1. In the same manner, the value ΔVdn at the carrier frequency Fn and the value ΔV at the carrier frequency Fm are centered around the carrier frequency F0.
The same operation is repeated for a plurality of points until Vd0m. Based on the above measurement results, the control unit 1 obtains a control table shown in FIG.

FIG. 6 is an explanatory diagram of the control table. In the figure, the transmission amplification factor A (F) is A (F) = (ΔVd / ΔVc)
And the control voltage change ΔVc at the carrier frequency F and F
This is a relationship with the M detection output ΔVd. A plurality of points are determined from the value A (Fn) at the carrier frequency Fn to the value A (Fm) at the carrier frequency Fm centering on the value A (F0) at the carrier frequency F0. Normalized transmission amplification factor a (F)
= A (F) / A (F0) is a value obtained by normalizing the transmission amplification factor A (F) with the value A (F0) at the carrier frequency F0. A plurality of points are obtained from the value a (Fn) at the carrier frequency Fn to the value a (Fm) at the carrier frequency Fm centering on the value 1 at the carrier frequency F0. The above result is stored in the adjustment value storage unit 5, and the FM modulated wave transmitter completes the preparation before transmission to the network.

The transmission operation of the FM modulated wave transmitter according to the present invention to the network will be described with reference to FIG. The audio or video input signal Si is input to the baseband unit 6.
At the same time, when the transmission control signal Sc is input to the control section 1 and the carrier frequency is designated as Fn, the FM modulated wave transmitter starts operating.

The control section 1 refers to the control table (FIG. 5) stored in the adjustment value storage section 5 to control the carrier frequency Fn.
Is obtained and applied to the control voltage input terminal Tc of the FM modulator 3. Baseband part 6
Converts the voice input signal Si into an electric signal SI and sends it to the baseband correction unit 2. At the same time, the control unit 1 refers to the control table of the adjustment value storage unit 5 to obtain a normalized amplification factor a (Fn) corresponding to the carrier frequency Fn. The normalized amplification factor a (Fn) is sent to the baseband correction unit 2 to divide the amplitude of the electric signal SI by a (Fn). By this calculation, when the input signal Si having a constant amplitude is input, it is possible to obtain an FM detection output Vd having no output deviation due to a change in the carrier frequency F. Returning to FIG. 5, this operation will be described again in terms of characteristics.

The FM modulator 3 starts operating at the point P1 in FIG. The transmission amplification factor at this point is: A (Fn) = ΔVdn / ΔVc (1) Similarly, the normalized transmission amplification factor is: a (Fn) = A (Fn) / A (F0) = (ΔVdn / ΔVc) ) ÷ (ΔVd0 / ΔVc) = ΔVdn / ΔVd0 (2) Therefore, when the electric signal SI is divided by the normalized transmission amplification factor a (Fn) in the baseband correction unit 2, the detection output Dn becomes
The following equation is obtained from the equations (1) and (2). Dn = SI × A (Fn) ÷ a (Fn) = SI × (ΔVd0 / ΔVc) Expression (3) Expression (3) shows that Dn is independent of the carrier frequency Fn. That is, it means that an FM modulated wave output Fout having no output deviation due to a change in the carrier frequency F can be obtained.

It is also possible to add a PLL circuit to the VCO of the specific example described above to operate the frequency control voltage Vc as a channel setting signal fixed at a plurality of predetermined frequencies.

[0030]

In the FM modulated wave transmitter according to the present invention, F
For a plurality of carrier frequencies F for which M-modulated wave transmission is scheduled, the output measuring unit 4 determines in advance the normalized transmission amplification factor a (F)
Is stored in the adjustment value storage unit 5. When the transmission of the FM modulated wave transmission starts, the control unit 1
Reads the normalized transmission amplification factor a (Fn) corresponding to the transmission carrier frequency Fn and sets the amplification factor of the baseband correction unit 2. By providing the above configuration, it is possible to obtain an FM modulated wave output Fout having no output deviation due to a change in the carrier frequency F.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM modulated wave transmitter according to the present invention.

FIG. 2 is an explanatory diagram of an FM modulator.

FIG. 3 is a relationship diagram between a control voltage of an FM modulator and a carrier frequency.

FIG. 4 is an explanatory diagram of a frequency discriminator using a resonance curve.

FIG. 5 is a diagram illustrating a relationship between a control voltage change and an FM detection output.

FIG. 6 is an explanatory diagram of a control table.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control part 2 Baseband correction part 3 FM modulator 4 Output measurement part 5 Adjustment value storage part 6 Baseband part 7 FM detector 8 Measuring instrument controller

Claims (1)

[Claims] 1. A baseband section for oscillating a test signal for measuring characteristics of an apparatus, a baseband correction section for increasing and decreasing the amplitude of a test signal output from the baseband section, and an output from the baseband correction section Accept the test signal,
An FM modulator that obtains an FM modulated wave output for an arbitrary carrier frequency at which FM modulated wave transmission is scheduled, and an output measurement that detects the FM modulated wave output output from the FM modulator and measures the amplitude of the detected output And an adjustment value storage for storing, as control data, an amplitude ratio of a detection output to an amplitude of the test signal in association with each carrier frequency at which FM modulated wave transmission is scheduled, based on a measurement result of the output measurement unit. And selecting a carrier frequency from the plurality of carrier frequencies and causing the FM modulator to transmit an FM modulated wave by referring to the control data stored in the adjustment value storage unit. An FM modulated wave transmitter, comprising: a control unit that operates the baseband correction unit so as to increase or decrease an input signal at an amplitude ratio of a detection output to an amplitude of a test signal.