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Instruments and measurement
Published in Stephen Sangwine, Electronic Components and Technology, 2018
Often these instruments can also count pulses or cycles of an input waveform (which can be useful in testing some digital circuits). These instruments are known as digital frequency meters, or counter/timers. A block diagram of a simple frequency meter, capable of measuring frequency and period, is shown in Figure 6.6. Although the instrument is digital, the input signal need not be. To allow for a range of input signal amplitudes, the input may be amplified or attenuated. A Schmitt trigger circuit, with a variable threshold level, then produces a digital waveform with a frequency equal to that of the input signal, provided that the threshold level is correctly set. Figure 6.7 shows how an incorrect threshold level can cause an erroneous frequency measurement. Some instruments have automatic control of the triggering level but are still prone to give false frequency readings if the input signal amplitude is too small or too large. A further problem can be excessive noise superimposed on the input waveform, which may be large enough to trigger the Schmitt trigger and therefore give a falsely high frequency reading. It is perhaps wise to examine the signal being measured with an oscilloscope, unless the signal is known to be relatively noise-free. The Schmitt trigger circuit is described by Senturia and Wedlock (1993), and in many other texts on circuits.
Programmable Logic Control Systems
Published in L. Ashok Kumar, M. Senthilkumar, Automation in Textile Machinery, 2018
L. Ashok Kumar, M. Senthilkumar
A Schmitt trigger will receive an input voltage between 0 and 5 V and convert it to 0 or 5 V. If the voltage is in an ambiguous range, about 1.5–3.5 V, it will be ignored. If a sensor has a TTL output, the PLC must use a TTL input card to read the values. If the TTL sensor is being used for other applications, it should be noted that the maximum current output is normally about 20 mA.
Fault-finding in microprocessor systems
Published in Stuart Anderson, Microprocessor Technology, 2012
The Schmitt trigger is an electronic circuit which switches between its output maximum and minimum at a critical level of input. The effect is that, regardless of the input, the output is a square wave (assuming that the input varies above and below the critical levels).
Developing a Piezoelectric Generator for Military Equipment – A Feasibility Study
Published in Electric Power Components and Systems, 2023
Karthikeyan Sathasivam, Ilhan Garip, Hayder Sharif, Jamal K. Abbas, Ali Adhab Hussein, Shahad K. Khaleel, Mustafa Asaad Rasol
The buck converter can operate in an uncontrolled way, that is, without monitoring the output voltage, in which a square wave generator generates the switch signal, and the output voltage is given by the expression Vo = DcycleVin. On the other hand, a control system can be added to the buck converter in which the MOSFET operation does not depend directly on an external signal. There are three modes of buck converter control: voltage control, current control, and hysteresis control. The voltage control and current control modes use an external signal generator [25]. Energy is spent generating a signal, while the hysteresis control mode does not need any external source. The controller with hysteresis can be implemented simply using a Schmitt trigger. The Schmitt trigger is an operational amplifier (AMPOP) fed by the voltages V AMP+ and VAMP− and two resistors. In one Schmitt triggers non-inverter. The inverter input of the AMPOP is connected to the ground of the converter, and the non-inverting input is connected a resistor R1 which is also connected to the converter output (Vo), and a resistor R2 which is also connected to the output of the AMPOP Vcontrol (Figure 10).
CMOS Schmitt – Inverter-Based Internal Reference Comparator Array for High Temperature Flash ADC
Published in IETE Journal of Research, 2023
George M. Joseph, T. A. Shahul Hameed
Schmitt trigger or regenerative comparator has traditionally been employed in communication and signal processing fields for improvements in on/off control and to plummeting the noise effects in triggering devices. CMOS versions of Schmitt trigger are widely used in VLSI solutions and a wide variety of design and implementations for CMOS Schmitt trigger circuits focusing at different applications, possessing different advantages have been proposed by many researchers. Dokic et al. [23] proposed three different versions of Schmitt trigger which include a circuit with three NMOS and three PMOS transistors, one with three NMOS and one PMOS transistor, and another circuit with three PMOS and one NMOS transistors. Steyaert et al. [24] proposed a CMOS Schmitt trigger made of five transistors with claims of process insensitivity. Pfister [25] introduced a Schmitt trigger with controllable hysteresis by introducing slight modification on [23]. Kim et al. [26] proposed a waveform reshaping circuit which is conceived as a substitute to the conventional Schmitt trigger with ratioless inverters, with claims of reduced standby power consumption and fast operating speeds. Al-Sarawi [27] introduced three different Schmitt trigger architectures with low power consumption and reduced hysteresis width. Pedroni [28] introduced inverter based Schmitt trigger architecture for low voltage and high-speed applications.
Experimental Verification of a New Oscillation-based Test Algorithm for Analog Circuits
Published in IETE Journal of Research, 2021
M. Parai, S. Srimani, K. Ghosh, H. Rahaman
The block diagram of the proposed method is depicted in Figure 1. In the normal mode of operation, the CUT behaves as per the conventional design of the filter circuit. Thus, during the normal mode of operation, switch S1 is closed, while the switches S2, S3 and S4 are open. During the test mode, the CUT is converted to a robust oscillator by incorporating positive feedback realized with the Schmitt trigger. Thus, in the test mode, switch S1 remains open and the switches S2, S3 and S4 are closed.