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FM Modulated IR Audio Transmission

FM Modulated IR Audio Transmission. By John Barton. The Chip. The chips I used were TSH512 and TSH511 from STMicroelectronics They modulate and demodulate, respectively, between analogue audio signals to FM signals. TSH512. Low Noise Amplifier (LNA). The front end of the circuit

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FM Modulated IR Audio Transmission

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  1. FM Modulated IR Audio Transmission By John Barton

  2. The Chip • The chips I used were TSH512 and TSH511 from STMicroelectronics • They modulate and demodulate, respectively, between analogue audio signals to FM signals

  3. TSH512

  4. Low Noise Amplifier (LNA) • The front end of the circuit • Gain of 0-40dB • Gain given by GLNA (dB) = 20.Log(1+RLNA2/RLNA1)

  5. Automatic Level Control (ALC) • Prevents over modulation • Reduces distortion and keeps reduced transmit spectrum • 20dB gain at 700mVp-p

  6. Voice Operated Transmit (VOX) • Mutes output when no audio signal is present • Can be bypassed if needed

  7. Voltage Controlled Oscillator (VCO) • Controls the internal oscillator • Has high power supply rejection ratio (PSRR)

  8. TSH511

  9. LNA • Another LNA amplifies the input from the IR receivers, this time with a gain of about 22dB

  10. AMP and LIM • Amplifier and limiter, with gains of 20dB and 60dB respectively amplify the signal and provide a constant amplitude to the FM Demodulator

  11. FM Demodulator • Demodulates the FM signal back into audio signals • Uses a tank circuit and a multiplier to help do this

  12. Squelch section • Prevents FM noise from getting to the speakers when no audio signal is present • Uses RC filter to isolate FM noise, then integrated with a capacitor to connected to MUTE-INT pin. Provides DC level based on noise • Mutes both outputs if noise is only signal present

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