JPH057649Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a high-speed waveform generator that generates high-speed signals for use in testing various analog circuits.

"Prior Art" A conventional waveform generator is shown in FIGS. 2 to 5. The waveform generation device shown in FIG. 2 is composed of two multipliers 1 and 2 and a waveform generation DA converter 3.

Multiplier 1 adds amplitude calibration data to waveform data SIG
Multiply AMC and use the multiplication result as waveform generation DA
The operation to apply to the converter 3 is performed.

Multiplier 2 multiplies the amplitude data AM by the calibration data CAL, and outputs the amplitude calibration data obtained as a result of the multiplication.
The operation of supplying AMC to the digital multiplier 1 is performed.

The waveform generation DA converter 3 applies a constant reference voltage ECON to the reference voltage terminal REF, performs DA conversion using this reference voltage as a reference voltage for waveform generation, and outputs an analog waveform.

In the example shown in Figure 3, waveform data SIG and amplitude data AM are given to multiplier 1, and the digital multiplication result is
Input SIAM to the waveform generation DA converter 3. 4
is given calibration data CAL, converts the calibration data into an analog voltage, applies the analog voltage to the reference voltage terminal REF of the DA converter 3 for waveform generation, and converts the analog signal output from the DA converter 3 for waveform generation. This figure shows an amplitude calibration DA converter that calibrates amplitude values.

The example in FIG. 4 shows a case in which the waveform generation DA converter 3 is placed at the front stage, and the level adjustment DA converter 5 is placed at the rear stage.

The level adjustment DA converter 5 is given the amplitude calibration data AMC obtained by multiplying the amplitude data AM and the calibration data CAL from the multiplier 2, and the level of the amplitude of the analog signal generated by the waveform generation DA converter 3 is adjusted. The structure is defined in the DA converter 5 for use in the DA converter 5.

In the example shown in FIG. 5, the calibration is performed by a DA converter 3 for waveform generation, a DA converter 4 for calibration data that applies a calibration voltage to its reference voltage terminal REF, and a DA converter 5 for level adjustment. An analog signal whose amplitude value has been calibrated by the DA converter 4 for level adjustment is applied to the reference voltage terminal REF of the DA converter 5 for level adjustment,
A case is shown in which amplitude data AM is applied to the digital input terminal of the level adjustment DA converter 5 and calibration is performed to define the amplitude value.

``Problem to be solved by the invention'' According to the signal generator shown in FIGS. 2 and 3, the amplitude data is added to the waveform data SIG in the multiplier 1.
Because of the structure in which AM is multiplied and the multiplication result is given to the DA converter 3, there is a drawback that when the amplitude value is reduced, the waveform quality of the analog signal output from the waveform generation DA converter 3 deteriorates.

In other words, for example, if the waveform generation DA converter 3 is an 8-bit DA converter, 8 bits are fully used for the maximum amplitude. Decreasing the amplitude gradually reduces the number of fully used bits. For this reason, as the amplitude becomes smaller, the number of fully used bits decreases and the resolution deteriorates. Since the change in analog voltage corresponding to one step of the smallest bit of the digital signal is constant, this results in a large rate of change in amplitude for one step, resulting in an increase in the distortion rate.

For this reason, the waveform generator with the structure shown in Figures 2 and 3 has a characteristic that the distortion rate of the output signal changes when the amplitude value is changed, and it is used for example in ICs that require a signal with a small distortion rate. It is not suitable for test equipment, etc.

According to the structure shown in Figures 4 and 5, for waveform generation.
Since the DA converter 3 always operates at full bits, the distortion rate will not worsen even if the amplitude value is reduced.

However, since a structure is adopted in which a DA-converted analog voltage signal is supplied from the waveform generation DA converter 3 to the reference voltage terminal REF of the level adjustment DA converter 5, the level adjustment DA converter 5 configured in this way operates at high speed. Can not do it.

As a result, the waveform generator shown in FIGS. 4 and 5 has the disadvantage that it is not possible to extract a high-speed signal faster than the response speed of the level adjustment DA converter 5.

"Means for Solving the Problem" In this invention, a variable attenuator for amplitude adjustment is provided after the DA converter for waveform generation, and the amplitude value can be changed by this variable attenuator. .

Therefore, according to this invention, the waveform generation DA converter can always be operated near full bits,
Even if the amplitude value is decreased, the distortion rate does not increase.

Further, since the variable attenuator is capable of high-speed response to signals, even if a high-speed signal is output from the waveform generation DA converter 3, this high-speed signal can be passed.

Therefore, according to this invention, various disadvantages described in the prior art can be eliminated, and an advantage can be obtained that a high-speed signal with a low distortion rate can be extracted.

``Example'' Figure 1 shows an example of this invention. The characteristic structure of this device is that a variable attenuator 6 is provided after the waveform generation DA converter 3, that this variable attenuator 6 is a logarithm variable attenuator, and that the amplitude data AM
and calibration data CAL are made into signals that vary according to the denbel (logarithm), and the control signal for the variable attenuator 6 is obtained by simply adding the amplitude data AM and the calibration data CAL.

The variable attenuator 6 includes a plurality of attenuation circuits 6A, 6B...
6N, and switches S ₁ , S ₂ . . . _SN for switching the attenuation circuits 6A, 6B .

The attenuation amounts of the attenuation circuits 6A to 6N are each weighted to change logarithmically. For example, the attenuation amount of the attenuation circuit 6A is 0.1 dB, the attenuation amount of 6B is 0.2 dB, the attenuation amount of 6C is 0.4 dB, ... 6N attenuation. Set the amount to 25.6dB.

The amplitude data AM and the calibration data CAL are digital signals whose amplitude values change according to decibels (dB). This amplitude data AM and the calibration data CAL are added by an adder 7, and the added value controls the on/off of switches S ₁ , S ₂ , S ₃ . . . _SN .

In other words, amplitude data AM and calibration data CAL are both
If it is 0 dB, all switches S ₁ to _SN are turned on and the attenuation amount is set to 0 dB.

When the added value of adder 7 reaches 0.1dB, the switch
_S1 is opened and an attenuation circuit 6A having an attenuation of 0.1 dB is connected to the circuit. In this case, for waveform generation.
The output of the DA converter 3 is attenuated by 0.1 dB and output.

When the added value of adder 7 reaches 0.2dB, the switch
S ₁ is closed and switch S ₂ is opened. As a result, the variable attenuator 6 has an attenuation amount of 0.2 dB.

When the added value of adder 7 reaches 0.3dB, switch _S1
and S ₂ are controlled to be off, and the variable attenuator 6 is
It will have an attenuation of 0.3dB.

In this way, the attenuation amount of adder 6 is determined by the amplitude data.
The amplitude value is controlled according to the sum of AM and calibration data CAL.

"Effect of the invention" As explained above, according to this invention, waveform generation is performed using the waveform generation DA converter 3, and amplitude control is controlled using the variable attenuator 6, so that the waveform generation The DA converter 3 can always generate waveforms using full bits. In particular, since the amplitude value is controlled by the variable attenuator 6, the number of bits used by the DA converter 3 does not change even if the amplitude value is changed.

Therefore, even if the amplitude is made smaller, the number of bits used by the DA converter 3 does not become smaller, so the distortion rate is kept constant. Therefore, even if the amplitude is changed, a signal with good waveform quality can be generated.

Furthermore, since the amplitude is adjusted by the variable attenuator 6, the variable attenuator 6 is simply constituted by a resistor network, so it has excellent high-speed response and can easily pass high-speed signals. Therefore, high-speed signals can be easily generated.

Furthermore, since the structure is such that the amplitude data AM and the calibration data CAL are added by the adder 7, the adder circuit has a simpler configuration than a multiplier and can be manufactured at low cost.

Therefore, according to this invention, it is possible to obtain a high-speed signal generation circuit that generates a high-quality signal with a low distortion rate, and it also has the advantage that it can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of this invention, and FIGS. 2 to 5 are block diagrams for explaining conventional techniques. 3...DA converter for waveform generation, 6...Variable attenuator, 7...Addition circuit, SIG...Waveform data, AM
...Amplitude data, CAL...Calibration data.

Claims (1)

[Scope of claim for utility model registration] DA converter for waveform generation and this DA for waveform generation
A logarithmically variable attenuator receives the DA conversion output of the converter and specifies the amplitude value of the DA conversion output for waveform generation, and a logarithmically variable attenuator that adds the amplitude data and calibration data and adjusts the logarithmically variable attenuator according to the added value. A high-speed waveform generator consisting of an adder that controls the amount of attenuation of an attenuator.