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9.2 Schmitt Trigger

Return. Next. 9.2 Schmitt Trigger. 9.2.1 Introduction. 数目众多的. 多功能性. 妨碍 , 牵制.

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9.2 Schmitt Trigger

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  1. Return Next 9.2 Schmitt Trigger 9.2.1 Introduction 数目众多的 多功能性 妨碍, 牵制 The Schmitt trigger has found many applications in numerous circuits, both analog and digital. The versatility of a TTL Schmitt is hampered by its narrow supply range, limited interface capability, low input impedance and unbalanced output characteristics. The Schmitt trigger could be built from discrete devices to satisfy a particular parameter, but this is a careful and sometimes time-consuming design. 阻抗 耗时的

  2. Return Back Next 9.2 Schmitt Trigger The CMOS Schmitt trigger has the following advantages: • High impedance input • Balanced input and output characteristics — Thresholds are typically symmetrical to 1⁄2 VCC — Outputs source and sink equal currents — Outputs drive to supply rails • Positive and negative-going thresholds show low variation with respect to temperature • Wide supply range (3V–15V), split supplies possible • Low power consumption, even during transitions • High noise immunity, 0.70 VCC typical 对称的, 均匀的 变化 免疫性

  3. Return Back Next 9.2 Schmitt Trigger 9.2.2 Schmitt Trigger’s Characteristic • Slowly changing input  fast transition time at the output • Different switching thresholds for positive and negative-going inputs • Hysteresis voltage = VT+- VT- • Application: • Trun a noisy or slowly varying input signal into a clean digital output signal • CMOS Schmitt Trigger: • The number of transistors in PUN and PDN will be changed by feedback  VT also changed

  4. R2 VI R1 Vo 1 1 Vo1 VI1 Return Back Next 9.2 Schmitt Trigger 9.2.3 Schmitt Trigger Consists of CMOS Gates Assume Vth = VDD/2 and R1<R2 Input VIis triangle wave

  5. VI VT+ VT- t Vo t Vo VI VT- VT+ Return Back Next 9.2 Schmitt Trigger (1) When From (1) we have (2)

  6. VI1↓, when The hysteresis is Return Back Next 9.2 Schmitt Trigger

  7. VI VT+ VT- t Vo t Return Back Next 9.2 Schmitt Trigger 9.2.3 The Applications of Schmitt Trigger • Transform of Waveform

  8. VI VT+ VT- Vo t Return Back Next 9.2 Schmitt Trigger • Pulse Plastic

  9. VI VT+ VT- Vo t Return Back Next 9.2 Schmitt Trigger • Pulse Amplitude Detection

  10. R Vo 1 VI VI VT+ VT- Vo T1 T2 t Return Back Next 9.2 Schmitt Trigger • Reform a Astable Multivibrator T=T1+T2=

  11. VR VR 1 VI VI VR VT+ VT- Vo Tw t Return Back 9.2 Schmitt Trigger • Reform a Monostable Multivibrator

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