JPS6122263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for magnifying and observing minute levels of periodically changing waveforms, such as measuring settling time of switching waveforms, amplifier step responses, etc. .

As shown in FIG. 1, a conventional waveform observation amplifier is a differential amplifier 3 that receives an observed waveform signal 2 from an observed signal source 1 and a comparison voltage 5 that is the output of a comparison voltage generator 4. The output 6, which is the amplified difference between the two inputs, was observed using an oscilloscope 8 synchronized with a synchronization signal 7 from the signal source 1. If the amplitude of signal 2 is small, there is no problem with this configuration, but when the amplitude of signal 2 becomes large, the first stage transistor of amplifier 3 turns on and off, which upsets the thermal balance and causes output 6 to includes the thermal response of amplifier 3, making it difficult to distinguish this thermal response from the waveform of signal 2, which has been a limitation of observation. In addition, when adjusting the comparison voltage 5 of the voltage generator 4 according to the level of the signal 2, it requires a great deal of effort to adjust the voltage value of several volts with an accuracy of about 100 μV, and the voltage generator 4 is also used as a standard The problem was that a noise filter was required in combination with an instrument-grade voltage generator.

An object of the present invention is to provide an amplifier that solves the problems of the conventional waveform observation amplifiers as described above.

In order to achieve the above object, the present invention uses a delay circuit that creates a pulse with a width T ₃ in which only the leading edge is delayed by an arbitrary time Δt from a synchronization signal synchronized with the observed signal, and a A loop return circuit is provided via a low-pass wave filter (hereinafter referred to as LPF) through which only direct current can pass, and during the delay pulse period, the observed signal is input to the differential amplifier, and at the same time, the loop return circuit is provided. The LPF output of is input to the differential amplifier as a comparison voltage, and the input terminals of the differential amplifier are short-circuited except during the delay pulse period.

FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 4 is a timing chart showing its operation. A synchronizing signal 11 output from the observed signal source 10 is supplied to a delay circuit 12 and an oscilloscope 25. As shown in FIG. 4, the pulse width of the synchronization signal 11 is T ₂ , but the output of the delay circuit 12 is a pulse with a width T ₃ in which only the leading edge is delayed by Δt compared to the synchronization signal. is sent to the switch drive circuit 14. By the output of the switch drive circuit 14, as shown in FIG.
The first switch 16 that transmits to the
The third switch 18 located between _the differential amplifier 22 and the amplifier 24 is turned on at timing T3 and turned off at times other than _T3 , and is a second switch that short-circuits the non-inverting input terminal 19 and the inverting input terminal 21 of the differential amplifier 22. Switch 17 is
Off at T _3. Drives on for periods other than T ₃ . The output signal 23 of the differential amplifier 22 is connected to the non-inverting input terminal of an amplifier 24 in the feedback circuit and to the input terminal of an oscilloscope 25. The output of the amplifier 24 is connected to the input of the LPF 20 through the third switch 18, and the output of the LPF 20 is connected to the inverting input terminal 21 of the differential amplifier 22. As can be seen in Fig. 4, if we pay attention to the timing of _T3 , the loop of amplifiers 22, 24, and LPF 20 operates so that the average level of the output signal 23 of the differential amplifier 22 becomes 0V, and the inversion of the differential amplifier 22 is performed. The signal to the input terminal 21 is the signal to the non-inverting input terminal 19, that is, the signal 1
5, the waveform moves toward the average level at timing T ₃ , and when both match, it becomes an equilibrium state and settles down. At timings other than T ₃ , the second switch 17 is connected between the two input terminals of the differential amplifier 22. Both non-inverting input terminal 19 and inverting input terminal 21 are short-circuited and become LPF.
Since the first switch 16 is opened and the observed signal source 10 is disconnected from the amplifier 22, the signal 15 from the observed signal source 10 has a large amplitude during periods other than _T3 . Amplifier 2 even when shaken
2 is not affected. Also during this period, LPF2
Since the input of 0 has been turned off by the third switch 18, the state up to that point is maintained. The amplifier 22 has input terminals 19 and 21 connected to the second switch 1.
Since they are connected to the same point by 7, they are in the active range, and no unnecessary thermal response will occur after entering the next timing of _T3 . of signal 15 by measuring the voltage at input 21 with a voltmeter.
The average voltage at T ₃ can be read with high precision, and by changing the delay time Δt of the delay circuit 12, various rising waveforms can be handled.

FIG. 3 is a diagram showing another embodiment of the present invention. A switch 26 is added between the observed signal source 10 and the first switch 16, a switch 27 is also added between the input of the connection point 29 of both switches, and the amplifier 2
A voltage generator 28 is connected to the inverting input terminal of 4. If the signal 15 has a large amplitude or a steep waveform, the circuit shown in FIG.
The signal 15 may leak to the input terminal 19 through the capacitance between the terminals of the switch 26 and saturate the amplifier 22.
By adding a switch 27 that operates in the same way as the second switch 17, the leakage phenomenon described above can be significantly reduced. Also, the voltage generator 28
By adjusting , the center voltage of the signal 23 at equilibrium can be arbitrarily set.

As explained above, conventionally it is possible to observe the settling state of a waveform with an amplitude of several volts at a speed of 1 μs or less.
However, in the present invention, a switch circuit is provided to prevent unnecessary voltage from being applied to the amplifier 22, so the speed of the waveform is reduced to the speed of the amplifier 22 itself (according to experimental results, it is approximately 100 ns). The recovery time for the switching noise of the switches 16 and 17 is obtained, and the waveform resolution is also within the noise range of the amplifier 22 (50 to 100 μV _pp ).
will be improved by. Further, since the adjustment of the comparison voltage is automated by the feedback circuit, an expensive voltage generator and its adjustment are not required, and the effects of the present invention are remarkable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional waveform observation amplifier, FIG. 2 is a diagram of one embodiment of the present invention, FIG. 3 is a diagram of another embodiment of the present invention, and FIG. 4 is a diagram of the implementation shown in FIG. 2. This is an example timing chart. 10... Observed signal source, 12... Delay circuit, 14...
Switch drive circuit, 16...first switch, 1
7...Second switch, 18...Third switch, 20...
LPF, 22...differential amplifier, 25...oscilloscope.

Claims (1)

[Claims] 1 A: a differential amplifier into which the observed signal is input to one input terminal via a first switch; B: an output from the differential amplifier is connected to the differential amplifier via a low-pass filter; C a second switch that shorts the two input terminals of the differential amplifier; D a pulse whose leading edge is delayed by an arbitrary period of time from a synchronization signal synchronized with the observed signal. The first switch is closed only during the pulse period generated by the delay circuit, and the observed signal is inputted to one terminal of the differential amplifier, and only during the pulse period other than the pulse period generated by the delay circuit. A waveform observation amplifier comprising switch driving means for closing the second switch to short-circuit the input terminals of the differential amplifier.