JP2532228B2 - Pulse shaper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pulse shaper that warps an input pulse into a pulse having a good settling characteristic and a steep leading edge.

[Technical background of the invention and its problems]

Since it is used as a signal source for performing highly accurate measurement, a pulse having a good settling characteristic may be required. However, for example, when the pulse amplitude is expressed by 8 bits, it takes a few times to settle to 1 LSB.
In order to obtain a palace with a characteristic of less than nS, less than 10nS for settling to 1LSB when expressed in 14 bits, and maintaining a constant value after settling, a pulse generator using a conventional amplifier is not suitable. It was enough. That is, in the conventional pulse generator, fluctuations such as undulations and level fluctuations were considerably large.

In order to solve this problem, the applicant of the present application filed Japanese Patent Application No. 61-20.
No. 5627 was filed as a circuit for providing a pulse which settles at high speed and does not have a slow level fluctuation after the settling as shown in FIG. 7, for example.

The basic idea of this circuit is to rectify the pulse given from the pulse generation source by a shaping circuit using a diode.

However, in such a configuration, the rising / falling edge of the output pulse is determined by the rising / falling edge of the pulse generator that supplies the shaped pulse. This was sufficient when a pulse response of several tens of nanoseconds was a problem. However, in order to measure even higher speed devices, there is an increasing need for a pulse shaper that can be sufficiently used even in a faster region of, for example, 10 nS or less.

Further, in the circuit of the above-mentioned patent application, a glitch may appear in the flat portion after the rising / falling edge of the output pulse. That is, in this circuit, the diode d _{2 which} is in the off state after the falling edge of the pulse from the pulse source P becomes capacitive. Therefore, if there is a fast pulse or glitch (for example, reflection due to mismatch of X point in FIG. 7), it passes through this capacitance to the load side.

[Object of the Invention]

The purpose of the present invention is to shape the input pulse,
It is an object of the present invention to provide a pulse shaper which has a good settling characteristic and has an extremely steep rise / fall and obtains a glitch-free pulse after the rise / fall.

[Outline of Invention]

In one embodiment of the present invention, the pulse output from the pulse generation source is applied to a pulse shaping circuit using a step recovery diode. This pulse shaping circuit generates a pulse whose rising or falling is extremely steep from a given pulse. By passing the pulse thus obtained through the die and cutting off the head at a constant level, it is possible to obtain a pulse having a good settling characteristic and an extremely fast rise or fall. A gallium arsenide Schottky barrier diode is preferably used as a diode for cutting off the output of the step recovery diode pulse shaping circuit at a constant level.

Example of Invention

FIG. 1 shows an embodiment of the pulse shaper of the present invention. First
FIG. 1A shows a configuration for generating a flat pulse on the high level side, and FIG. 1B shows a configuration for generating a flat pulse on the low level side. In the figure, Vs and Vs 'are pulse generators, Rs and Rs' are the internal resistances of the pulse generators, Ro is the output resistance of the pulse shaper, and R _L is the load resistance.
System. In addition, Do is a step recovery diode,
D ₁ and D ₂ are gallium arsenide Schottky barrier diodes. −V _N , + V _P applies a bias voltage to the step recovery diode Do, and an appropriate bias current to the Schottky barrier diode D ₁ or D ₂ by the resistor R _B. The capacitor Co is a bypass capacitor for the bias power supply.

The circuit configurations (a) and (b) in FIG. 1 are basically the same in operation except that the polarities are different. Therefore, only (a) will be described below.

FIG. 2 shows changes in the voltages of the main parts in the circuit configuration shown in FIG. In FIG. 2, first, the pulse generator Vs outputs the low-level voltage Lo. At this time, the step recovery diode Do is turned on. Further, since the Schottky barrier diode D ₂ is also turned on, a current flows through the load resistance R _L. As a result, the output voltage Vo of the pulse shaper becomes a negative voltage (−I _F2
(Ro // _RL )). Incidentally, I _F2 is the current when Schottky barrier diode D ₂ is in the ON state. The voltage V _Fn and the current I _Fn when the diode Dn (n = 0, 1, 2) is in the ON state are defined as shown in FIG.

Next, at time t ₀ , the output voltage of the pulse generation source Vs becomes Hi.
However, the step recovery diode Do is not immediately turned off, but is in a low impedance state (called a short state) for a period of time to. This time to is determined by the minority carrier lifetime of the step recovery diode used (typically 10 to 100 ns) and the current I _FO flowing through the step recovery diode when in the on state. Therefore, the rise of the output of the pulse generation source Vs has only to be shorter than to, so that a general-purpose pulse generator or the like can be sufficiently used.

After the elapse of time to (time t ₁ ), when all the charges in the step recovery diode Do are released, this diode Do snaps off and the voltage Vi rises sharply. This rise speed usually does not require 100ps to produce a pulse of about 10V. As the voltage Vi rises, the Schottky barrier diode D ₁ is turned on, and at the same time the Schottky barrier diode D ₂ is turned off. Since both diodes are gallium arsenide Schottky barrier diodes, the voltage Vo rises rapidly from a negative voltage to zero. After this, the load resistance R _L
When you look into the pulse shaper from, it looks like a signal source with output impedance Ro and voltage 0V. This results in a pulse that is extremely flat on the high level side and has a very fast rise. Furthermore, even if there is reflection due to the rise of the voltage of the Vs output of the pulse generation source, if this falls within the time to, the glitch does not appear in the flat portion of the voltage Vo.

When the Schottky barrier diode D ₂ moves from the on state to the off state, the inductance and capacitance components of the diode cause ringing. Therefore, as a Schottky barrier diode,
It is preferable to use one having a sufficiently small junction capacitance and a small size. Current gallium arsenide technology provides Schottky barrier diodes with an inductance of 0.2nH or less and a capacitance (junction capacitance and package capacitance) of 50fF or less. Therefore, if the output resistance Ro is a pure resistance, it is possible to obtain a pulse with very small ringing and very fast settling (1 nS or less).

In FIG. 2, the output of the pulse generation source Vs is shown as a single step waveform, but it goes without saying that a repetitive waveform or the like may be applied. Further, when the pulse shaper and the load are separated from each other, they can be connected by an impedance-matched transmission line.

Now, when actually creating a pulse shaper as described above, for example, if one wants to obtain characteristics with a rise / fall time of 100 pS or less and a settling time of 1 nS or less, ideally, the diode die The chip, the thin film resistor, and the chip / capacitor may be arranged on the sapphire substrate and then housed in a brass case that has been milled, for example, and may be configured using microwave technology.

However, the output of the pulse shaper of the present invention, which is made by considering the high frequency characteristics by appropriately shielding by using a step recovery diode, a gallium arsenide Schottky barrier diode, etc. which are normally available discrete components, An example is shown in FIG. In this measurement, 1M
The repetitive waveform of Hz was applied to a pulse shaper, and the output was sampled and digitized by a sampler with a bandwidth of 1 GHz. As can be seen from the figure, an extremely steep rise was obtained and settling was already stopped. In addition,
The rise of the output seems to be slightly rounded because the bandwidth of the sampler is narrow, and the rise of the output itself is steeper.

As mentioned above, there is a sharp step with a steep rise.
Once the pulse is obtained, it can be applied to the TDR. As shown in FIG. 5, the output of the pulse shaper prepared as above and the input of the sampler are connected by a T connector of SMA, and a cable with a length of 1 m and an open tip is connected to this. The measured waveform when this connection is made is shown in FIG. As can be seen from the figure, a clear reflection waveform is observed with some ringing. When the conventional pulse shaper was used, the rise was not so fast, so the waveform at the staircase was blunted. Conventionally, averaging processing or the like has been performed in order to perform accurate timing measurement, but this is no longer necessary by using the pulse shaper of the present invention. Further, when impedance (for example, capacitance) at the tip of the cable is generated, the impedance can be calculated by the waveform shaper, but by using the waveform shaper of the present invention, fairly accurate impedance measurement is possible.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a pulse shaper having both a good settling characteristic and a sharp rise / fall. Therefore, it is possible to obtain a signal for measuring various high speed devices and other signals. It can be used as a signal source for generating a reference signal.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a diagram showing a voltage change etc. of a main part of the embodiment of the present invention shown in FIG. 1, and FIG. 3 is an explanation of current and voltage of a diode. Figure 4
FIG. 5 is a diagram showing an example of measurement of characteristics of a pulse shaper actually made according to the present invention, FIG. 5 is a diagram showing a configuration of an application example of the pulse shaper of the present invention, and FIG. 6 is a diagram showing the configuration of FIG. FIG. 7 is a diagram showing an example of measurement results, and FIG. 7 is a diagram showing a conventional example. Vs, Vs ′: pulse source, Do: step recovery diode, D ₁ , D ₂ : gallium arsenide Schottky barrier
diode.

Claims (2)

(57) [Claims] 1. A step recovery diode means connected between an input terminal and a bias power source, and first and second diode means connected in series between the input terminal and an output terminal with opposite polarities. A bias resistance means connected between a common connection point of the first and second diode means and the bias power supply; an output resistance means connected between the output end and a ground potential; And a power supply bypass capacitor means connected between the ground potential and the ground potential, and is driven by a pulse generation source to output a pulse having a steep rise or fall and at least one peak level being substantially flat. A pulse shaper characterized by: 2. The pulse shaper according to claim 1, wherein the first and second diode means are gallium arsenide Schottky barrier diodes.