JPS6145611A - Synchronizing rectifier circuit - Google Patents

Abstract

PURPOSE:To increase the modulation frequency without increasing an error due to glitch by using a synchronizing signal so as to demodulate only a stable portion of a pulse amplitude modulation signal thereby applying synchronizing rectification. CONSTITUTION:A carrier signal (b) is inputted to a monostable multivibrator 7 via a delay circuit 6 and the output of the monostable multivibrator 7 switches a switch 3 as a synchronizing signal (f). The signal (f) is formed to be risen after a delay time Td after leading of the signal (b) and to be fallen down after a pulse width TM. The relation of time Td+pulse width TM<= pulse width Tc of signal (b) is satisfied. Thus, only a stable portion of a signal (c) is given to a low-pass filter 4. Thus, generation of glitch when the switch 3 is turned on is prevented and the modulation frequency is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a synchronous rectification circuit, particularly to a synchronous rectification circuit used in a demodulation circuit such as a chopper amplifier or an isolation amplifier.

[Technical Background of the Invention] In a chopper amplifier or isolation amplifier, the input signal voltage is pulse amplitude modulated (PAN) by a carrier signal, and the resulting modulated signal is opened and closed in synchronization with the carrier signal. A synchronous rectification method is used in which the signal is demodulated by

FIG. 3 shows an example of the configuration of a chopper amplifier using a conventional synchronous rectifier circuit. In FIG. 3, 1 is a pulse amplitude modulator and 2 is a carrier signal generator. A switch 3 opens and closes in synchronization with the carrier signal, and synchronously rectifies the pulse amplitude modulated signal obtained by the pulse amplitude modulator 1. 4 is a low-pass filter that removes high frequency components from the demodulated signal obtained by synchronous rectification. 5 is a buffer that amplifies the output of the low-pass filter 4.

In a chopper amplifier with such a configuration, the operating waveforms of each section are as shown in Figure 4. The symbols a to e in FIG. 4 correspond to the symbols a to e in FIG. The demodulated signal e which has been synchronously rectified by opening and closing is the output signal of the low-pass filter 4. The output voltage of the buffer 5 is the same as e, so its description will be omitted. Here, the waveforms shown by dotted lines in Fig. 4c, d, and e are the input voltage a
It can be seen that the output signal e of the low-pass filter 4 has an error.

[Problems with the Background Art] Generally, the pulse amplitude modulated signal C has a response delay determined by the slew rate of the pulse amplitude modulator 1, but the operating time of the switch 3 is short compared to this. Therefore, if the switch 3 is turned on when the carrier signal is at a torque level, a spike-like transient waveform, ie, a glitch, as shown in FIG. 4d occurs in the demodulated signal. This glitch is the cause of the above-mentioned error, and the higher the modulation frequency, the larger the error caused by the glitch. Therefore, in the configuration shown in Fig. 3, the frequency of the carrier signal generator 2 is currently lowered to prevent the occurrence of errors, but as a result, the frequency band of the entire chopper amplifier is significantly reduced. is occurring. In the example so far, the modulation frequency is 10KHz, and the frequency band (
-3db) I KHz is typical. Also, the modulation frequency of isolation amplifiers is lowered for the same reason, but since isolation amplifiers use isolation transformers, they have the disadvantage of lowering the frequency band and increasing the size of the transformer. .

[Purpose of the Invention] The present invention has been made to solve the above problems, and its purpose is to provide a synchronous rectifier circuit that has a wide frequency band and can make chopper amplifiers and isolation amplifiers smaller. There is.

[Summary of the Invention] In the present invention, by controlling the timing at which the above-mentioned switch 3 is turned on, only the stable part of the pulse amplitude modulation signal is demodulated, thereby preventing the occurrence of glitches that cause errors. It provides a synchronous rectifier circuit with a configuration of

[Embodiments of the Invention] Examples will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a synchronous rectifier circuit according to the present invention. 1st
In the figure, the same parts as in FIG. 3 are given the same reference numerals, and their explanation will be omitted.

The carrier signal is input to the monostable multivibrator 7 via the delay circuit 6, and the monostable multivibrator 7
The output is configured to open and close the switch 3 as a synchronization signal f. The other configurations are the same as in FIG. 3. FIG. 2 shows operating waveforms of each part in FIG. 1, and symbols a to f correspond to symbols a to f in FIG. 1, respectively. In addition, Figure 2a
-C has exactly the same waveform as FIG. 4a-C.

According to this embodiment, when the carrier signal S rises from 1 lvl to 1 lvl, the synchronizing signal f rises after the delay time Td by the delay circuit 6 has elapsed, and the switch 3 is turned on. Here, by selecting an appropriate value for the delay time Ta and setting it so that only the stable portion of the pulse amplitude modulation signal C is transmitted to the low-pass filter 4, it is possible to prevent glitches from occurring when the switch 3 is turned on. . For example, if the slew rate of the pulse amplitude modulator 1 is 20V/IIs and the maximum amplitude of the pulse amplitude modulation signal C is 10V I)-D, the time during which a glitch can occur is 0.57715, so Ta
>0.5 IIs can prevent glitches. Furthermore, if the operating time of the monostable multivibrator 7 is set to Ta + TM≦Tc with respect to the pulse width Tc of the carrier signal S, the synchronizing signal f is generated before the fall of the carrier signal S.
becomes the torque level, and the switch 3 is turned off while the pulse amplitude modulation signal C is in a stable state. Therefore, glitches when the switch 3 is turned off can also be prevented.

As a result of the above operation, the demodulated signal has a waveform like d', and it can be seen that glitches have been completely removed when compared with FIG. 4d. Furthermore, the error in the output e' of the low-pass filter 4 is significantly reduced, and the error due to the operating principle becomes zero with respect to the DC input voltage. As described above, in this embodiment, since glitches do not occur, there is no possibility that errors will increase even if the modulation frequency is increased. Therefore, conventionally 10KHz
The modulation frequency (carrier signal frequency) that was about 5K
It is possible to reduce the frequency bandwidth of the chopper amplifier or isolation amplifier to about H7.
It can be doubled. Regarding the modulation frequency, there is a limit due to the characteristics of the pulse amplitude modulator 1 and the switch 3, so 50 KHz F 1 degree is currently appropriate, but if the frequency of the pulse amplitude modulator 1 etc. advances, the modulation frequency may be further increased. is also possible. In addition, in the case of an isolation amplifier, if the modulation frequency is increased five times, the core cross-sectional area of the isolation transformer can be reduced to 175 (assuming the number of turns is constant), so it is possible to significantly reduce the size.

As for the delay circuit, it can be easily realized by using a CR temporary delay system to delay the rise time of the monostable multivibrator 7 up to the threshold voltage, or by using a pulse delay line. .

In the embodiment shown in FIG. 1, the switch 3 is turned on when the synchronization signal f is 1 level. A synchronous rectifier circuit similar to that of the above embodiment can also be used.

[Effects of the Invention] As explained above, according to the present invention, errors due to glitches increase due to the configuration in which synchronous rectification is performed using a synchronous signal that can demodulate only the stable portion of a pulse amplitude modulation signal. It becomes possible to increase the modulation frequency without increasing the frequency. Therefore, when used in a chopper amplifier, an isolation amplifier, etc., the frequency band width can be expanded and the isolation transformer can be significantly downsized.

[Brief explanation of the drawing]

Fig. 1 is a chopper amplifier block diagram using an embodiment of the synchronous rectifier circuit according to the present invention, Fig. 2 is a time chart showing the operating waveforms of Fig. 1, and Fig. 3 is a chopper amplifier block diagram using an embodiment of the synchronous rectifier circuit according to the present invention. The chopper amplifier block diagram, FIG. 4, is a time chart showing the operating waveforms of FIG. 3. 1...Pulse amplitude modulator 2...Carrier signal generator 3...Switch 4...Low pass filter 5...Buffer 6...Delay circuit 7...
・Monostable Multivibrator (7317) Representative Patent Attorney Kensuke Norichika (and 1 other person) Child 1 figure Person 2 figure

Claims (3)

[Claims] (1) In a synchronous rectifier circuit that pulse-amplitude modulates an input signal using a carrier signal and rectifies the pulse-amplitude modulated signal periodically with the carrier signal, a synchronous signal synchronized with the carrier signal is generated to perform the rectification operation. In addition, the synchronization signal is formed to rise after a delay time T_a after the rise of the carrier signal and fall after a pulse width T_M has elapsed, and has a relationship of T_a+T_M≦T_c with respect to the pulse width T_c of the carrier signal. A periodic rectifier circuit characterized by being set to satisfy the following conditions. (2) The synchronous rectifier circuit according to claim 1, which uses an inverted signal of the synchronous signal as the synchronous signal. (3) The synchronous rectifier circuit according to claim 1 or 2, wherein the synchronous signal is generated by a delay circuit and a monostable multivibrator.