| 摘要 |
<p>Improved radio transmitter modulation control circuitry which significantly increases the average power of the modulating signal, resulting in enhanced audio signal quality since the signal-to-noise ratio is likewise increased. The inventive modulation control circuitry includes a microphone (110), audio amplifier (120), splatter filter (130), modulator (150), potentiometer (140), oscillator and transmitter (180), and antenna (190). The audio amplifier (120) further includes an operational amplifier (160) having an input resistor (162) coupled via capacitor (168) to microphone (110), a phase-lag filter (170) coupled to the output of the operational amplifier (160), and a feedback resistor (161) coupled between the filter (170) and the input resistor (162). When driven into amplitude limiting, the phase and amplitude of harmonic signals from the operational amplifier (160) are altered by phase-lag filter (170) to produce a waveform similar to that shown in Fig. 2. When operated linearly, the audio amplifier (120) has a flat frequency response, the filter (170) having no effect since it is in the feedback loop. The improved modulation control circuitry of the present invention can be advantageously utilized in both amplitude and frequency modulated radios (100) for enhancing the audio signal quality thereof.</p> |
