JP2936284B2 - Signal generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a signal generator, and more particularly, to a signal generator used as a signal source when measuring a frequency characteristic of a video amplifier.

<Problems to be Solved with Conventional Technique> In a television or a personal computer monitor, a video amplifier is used to amplify a video signal to a required size and supply it to a cathode of a CRT.

As shown in FIG. 4, when the level of the horizontal synchronizing pulse (negative pulse) is 0 volt, the level of 0.3 volt is defined as black level and the level of 1.0 volt is defined as white level. Contains video components for one raster.

In addition, since the cathode potential and the luminance in a general cathode fast-moving CRT are in inverse proportion, an inverting amplifier is used as a video amplifier, but from 0 volt to 1.
In order to amplify a 0 volt input signal by DC, a stable power supply of both polarities is required, and the voltage of each level of the input video signal must be a specified absolute voltage. And the versatility of the input signal level.

Therefore, a clamp-type video amplifier 1 as shown in FIG. 5 is used as an actual video amplifier.

This video amplifier 1 is connected to a capacitor C1 from an input terminal 1a.
And a video signal input via the resistor R1 are amplified and output to the output terminal 1b by the DC inverting amplifier 2 of a single power supply, the output voltage is divided by the resistors R2 and R3, and a predetermined reference voltage Vr
Is input to the differential amplifier 3, the differential output is charged to the capacitor C2 via the switch 4 which is turned on by the clamp signal input from the clamp signal input terminal 1c, and the charged voltage is supplied via the resistor R4. And the connection point between the capacitor C1 and the resistor R1.

The clamp signal is output from another circuit to the video amplifier 1 every predetermined black level time (pedestal time Tp) after the horizontal synchronization pulse included in the video signal. The capacitor C2 is charged in a direction in which the divided output of the output voltage becomes equal to the reference voltage Vr.

Therefore, if the reference voltage Vr is set in advance to a value obtained by dividing the normal black level output voltage by the resistors R2 and R3, the operating point of the DC inverting amplifier 2 determines the operating point of the video signal input via the capacitor C1. It is possible to prevent the fluctuation following the average value change of the video component, and to perform a stable amplification operation.

Such a video amplifier is required to have a frequency characteristic necessary for faithfully amplifying a wideband video component.

For this reason, in a line for producing this type of video amplifier, the frequency characteristics thereof are measured and adjusted.

Generally, the frequency characteristics of an amplifier are measured by inputting a signal from a signal generator to the amplifier under test and observing the level change of the amplifier output with respect to the frequency of the input signal, but over a wide video band up to several tens of MHz. The output signal of the conventional signal generator for generating a signal is an AC-coupled output, and even if the output signal is input to the video amplifier 1 of the conventional technology, the charge control for the capacitor C2 is not performed. The operating point of the amplifier 2 is not stable, and
It is impossible to perform a normal measurement because the output is saturated by a negative input signal component.

This is a measurement performed by a network analyzer having a spectrum analyzer section that sweeps and receives and detects an output signal from the circuit under test and a signal generator that inputs a signal having the same frequency as the sweep reception frequency to the circuit under test. The same applies to the case.

Therefore, using such a conventional signal generator,
When measuring the frequency characteristics of the clamp type video amplifier, as shown in FIG. 6, the capacitor C1 on the input side of the video amplifier 1 is short-circuited, the connection of the resistor R4 is cut off, and the signal generator is connected. A method has been adopted in which a DC voltage is superimposed on a signal from 10 by a DC superimposing circuit 5 and input to the video amplifier 1.

The DC superimposing circuit 5 superimposes the DC voltage from the DC power supply 6 on the signal from the signal generator 10 received by the capacitor C5 via the high-frequency choke coil L1. The point can be set to an optimum state by the voltage of the DC power supply 6.

However, such a method requires complicated operations such as short-circuiting, cutting, and repairing the video amplifier.

Also, the operation of the clamp function cannot be confirmed,
There is a problem that the frequency characteristics of the DC superposition circuit affect the measurement result.

Note that if the capacitor C1 on the input side of the video amplifier 1 is short-circuited and the connection of the resistor R4 is disconnected to measure the frequency characteristics, the video amplifier cannot operate in the actual operation state. There is also a problem that the frequency characteristics of the video amplifier in a state where the offset voltage is changed cannot be known.

An object of the present invention is to provide a signal generator that solves these problems.

<Means for Solving the Problems> In order to solve the problems, a signal generation device of the present invention includes: a signal generation unit that outputs a signal having a frequency corresponding to a control signal; and a signal in a desired frequency range from the signal generation unit. Control signal output means for repeatedly outputting a control signal for sweep output to a signal generator, and a first synchronization pulse synchronized with a repetition cycle of the sweep of the control signal from the end of the sweep to the start of the next sweep A first synchronizing pulse output means for outputting the second synchronizing pulse synchronized with the repetition period of the sweep of the control signal, and a second synchronizing pulse outputting while the first synchronizing pulse is being output Output means, a DC voltage source for outputting a predetermined DC voltage, and output switching means for switching and outputting the DC voltage of the DC voltage source in place of the output signal from the signal generator while receiving the first synchronization pulse And I have.

<Operation> Therefore, in this signal generator, a DC voltage from a DC voltage source is output instead of this signal every time the sweep of a signal in a desired frequency range ends, and this DC voltage is output. Since the second synchronization pulse is output in between,
If the output signal from the output switching means is input to the clamp-type video amplifier and the second synchronization pulse is input as the clamp signal, the frequency characteristics of the clamp-type video amplifier can be measured.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a network analyzer 20 having a signal generator according to one embodiment.

In FIG. 1, reference numeral 21 denotes a VCO (voltage controlled oscillator) 22 which oscillates and outputs a signal having a frequency corresponding to the control voltage Vc;
This is a signal generation unit configured with a frequency conversion circuit 23 that converts the output frequency Fo of the CO22 into a lower frequency by an IF frequency (Fi) described later and outputs the converted frequency.

24, the frequency of the signal output from the signal generator 21 is
This is a control signal output unit that repeatedly outputs a control voltage Vc for sweeping a desired range in a desired cycle.

The control signal output unit 24 divides the signal from the reference oscillator 25 by the divider 26, and outputs a control signal that changes in a sawtooth waveform while the divided pulse is at the “H” level. Output from 27.

28 is a sweep cycle setting means for setting a frequency division ratio for determining a sweep cycle of a control signal swept in a sawtooth waveform in the frequency divider 26, and 29 is a sweep of a control signal swept in a sawtooth waveform. This is a sweep range setting means for setting a start voltage and an amplitude.

Reference numeral 30 denotes a first synchronization pulse output unit that outputs a first synchronization pulse synchronized with the output of the frequency divider 26.
A first delay circuit 31 to time T ₁ delay, the "L" level pulse of the pulse width T ₂ from falling of the divided pulses is the delay, the first one-shot multi-output as the first synchronization pulse The circuit 32 is configured.

33 is a second synchronizing pulse output unit, similarly to the first synchronizing pulse output unit 30, the division pulse T ₃ hours (T ₁ <T ₃ <
T ₁ + T _2/2) and the second delay circuit 34 for delaying, delayed dividing pulses of the pulse from the falling width _{T 4 (T 4 <T 1} + T 2 -
The second one-shot multi-circuit 35 outputs the "L" level pulse of T ₃ ) as a second synchronization pulse.

36 is a DC voltage source that generates the DC voltage Vd set by the voltage setting means 37, and 38 is the DC voltage Vd and a signal generation unit.
An output switch for switching between an output signal from a frequency conversion circuit 21 and an output switch. The output switch outputs a DC voltage Vd to a first output terminal 39 while receiving a first synchronization pulse.
While the output from the synchronization pulse output unit 30 is at “H” level,
The signal from the signal generator 21 is output.

Reference numeral 40 denotes a second output terminal for outputting a signal from the second synchronization pulse output unit 33.

Reference numeral 42 denotes a sweep receiving unit that receives a signal input from the input terminal 41 in a sweep manner. The mixer 43 mixes the input signal with the output signal of the VCO 22. IF that passes only the signal of the predetermined band
It comprises a filter 44 and a detection circuit 45 for detecting an output signal from the IF filter 44.

Reference numeral 46 denotes a display device in which the control signal from the control signal generation circuit 27 is input to the X-axis and the output from the detection circuit 45 is input to the Y-axis. Is formed so as not to be displayed.

Next, the operation when the frequency characteristic of the clamp-type video amplifier 1 is measured by the network analyzer 20 will be described.

As shown in FIG. 1, the input terminal 1 of the video amplifier 1
a, a first output terminal 39, an input terminal 41, and a second output terminal 40 are connected to the output terminal 1b and the clamp signal input terminal 1c, respectively.

Next, the values corresponding to the video amplifier 1 are set in the sweep cycle setting means 28, the sweep range setting means 29 and the voltage setting means 37, respectively, and the measurement is started. The frequency-divided pulse shown in FIG.
It is output to 27, from the control signal generating circuit 27, a control signal which varies in sawtooth from voltages V ₁ to V ₂ as shown in the same figure (b) is repeatedly outputted.

Further, from the first synchronization pulse output section 30, as shown in the figure (c), dividing the first synchronization pulse is output changeover switch width T ₂ delayed by T ₁ from falling of the pulse
Since the output 38, the output terminal 39, after the sweep signal from the frequencies F _1, as shown in the same (d) of FIG until the frequency F ₂ is output, the DC voltage Vd is T ₂ hours Output Will be done.

Since the crank signal input terminal 1c of the video amplifier 1, the second synchronizing pulse having a pulse width T ₄ as shown in the same figure (e) is output while the direct-current voltage Vd is output, the video amplifier At 1, the DC voltage Vd is clamped at a pedestal level (black level).

Therefore, for example, if the signal amplitude (peak-to-peak voltage) from the signal generator 21 is set to 0.7 volt (white level voltage-black level voltage) and Vd is set to -0.35 volt, the video amplifier 1
The frequency characteristic can be measured using a signal having the maximum amplitude allowed for the signal.

The output of the video amplifier 1 is detected by the sweep receiver 42,
For example, as shown in FIG.
Will be displayed on the video amplifier 1
Can be easily confirmed.

Also, when the DC voltage Vd generated by the DC voltage source 36 is changed, the input signal offset voltage of the video amplifier 1 is equivalently changed without changing the offset voltage of the output from the frequency conversion circuit 23. Become. For this reason,
The frequency characteristics when the operating point of the video amplifier 1 is changed can also be confirmed.

<Other embodiments of the present invention> In the above embodiments, the network analyzer having the signal generator of the present invention as a signal line has been described. Needless to say, the signal output unit 24, the first and second synchronization pulse output units 30 and 33, the output changeover switch 38, and the DC voltage source 36 alone may be used.

Further, in the above embodiment, the embodiment of the present invention has been described by using the analog sweep type network analyzer. However, the present invention can be similarly applied to a network analyzer and a signal generator based on digital sweep control. .

<Effect of the Present Invention> As described above, the signal generator of the present invention can output a predetermined DC voltage instead of the sweep signal every time one sweep is completed, and Since the second synchronizing signal can be output during output, the frequency characteristics of the video amplifier can be measured and the change in the frequency characteristics of the video amplifier due to the offset change of the input voltage can be measured without processing or repairing the circuit in the video amplifier. The operation can be easily performed with the clamp function activated, and there is no influence on the measurement by the external connection of the DC weight circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a network analyzer having a signal generator according to one embodiment of the present invention, FIG. 2 is a signal diagram of each part for explaining the operation of one embodiment, and FIG. FIG. 8 is a diagram showing a display result by the device of one embodiment. FIG. 4 is a diagram showing a video signal, FIG. 5 is a circuit diagram of a clamp-type video amplifier, and FIG. 6 is a diagram showing a conventional method for measuring a frequency characteristic of the clamp-type video amplifier. 1 ... Video amplifier, 20 ... Network analyzer,
21 ... Signal generation unit, 24 ... Control signal output unit, 30 ... First
A second synchronization pulse output unit, 33...
36 ... DC voltage source, 38 ... Output switching means, 42 ... Sweep receiver, 46 ... Display device.

Claims (1)

(57) [Claims] 1. A signal generator for outputting a signal having a frequency corresponding to a control signal, and a control signal for causing a signal in a desired frequency range to be swept and output from the signal generator, is repeatedly transmitted to the signal generator. Control signal output means for outputting, a first synchronization pulse output means for outputting a first synchronization pulse synchronized with a repetition cycle of the sweep of the control signal from the end of the sweep to the start of the next sweep, and the control A second synchronizing pulse output means for outputting a second synchronizing pulse synchronized with a repetition cycle of signal sweep while the first synchronizing pulse is being output; a DC voltage source for outputting a predetermined DC voltage And an output switching means for switching and outputting the DC voltage of the DC voltage source instead of the output signal from the signal generating unit while receiving the first synchronization pulse. Generator.