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US4991227A Squelch circuit with variable squelch tail and variable hysteresis 失效
具有可变静噪尾部和可变滞后的静噪电路

  • 专利标题： Squelch circuit with variable squelch tail and variable hysteresis
  • 专利标题（中）： 具有可变静噪尾部和可变滞后的静噪电路
  • 申请号： US141853
    申请日： 1988-01-11
  • 公开(公告)号： US4991227A
    公开(公告)日： 1991-02-05
  • 发明人: Walter H. Kehler, Jr.
  • 申请人： Walter H. Kehler, Jr.
  • 申请人地址： IL Schaumburg
  • 专利权人： Motorola, Inc.
  • 当前专利权人： Motorola, Inc.
  • 当前专利权人地址： IL Schaumburg
  • 主分类号： H03G3/34
  • IPC分类号： H03G3/34 ;  H04B1/10
Squelch circuit with variable squelch tail and variable hysteresis
摘要：
The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is also variable. If, immediately before the fade, the received signal strength exceeds a predetermined trigger level (Vtrg) the threshold level is raised. A buffer amplifier (102) charges a capacitor (C) to a voltage which is proportional to the strength of a received carrier. If the carrier fades below a threshold (Vth2 or Vth3, the buffer is disabled and the capacitor slowly discharges through a resistor (R). When the voltage at the capacitor crosses a reference voltage (Vref1) the output of a comparator (104) switches, thereby deactivating the receiver's audio amplifier. If the voltage at the buffer output is within a specified range, a feedback control circuit (112) switches a variable hysteresis feedback circuit (110) such that the negative-going threshold of the comparator (106) is switched from one threshold level (Vth2) to another (Vth3).
摘要（中）：

在接收到的载波的信号强度衰落到阈值以下之前，静噪电路维持无线电接收机的音频放大器有效的时间与紧接在衰落之前的接收到的载波的强度成反比。 该阈值水平也是可变的。 如果在衰减之前，接收到的信号强度超过预定的触发电平（Vtrg），则阈值电平升高。 缓冲放大器（102）将电容器（C）充电到与所接收的载体的强度成比例的电压。 如果载波衰减到阈值以下（Vth2或Vth3，缓冲器被禁止，电容器通过电阻器（R）缓慢放电，当电容器的电压跨过参考电压（Vref1）时，比较器（104）的输出开关 如果缓冲器输出端的电压在规定的范围内，则反馈控制电路（112）切换可变滞后反馈电路（110），使得比较器（106）的负向阈值 从一个阈值电平（Vth2）切换到另一个（Vth3）。

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