Self Study, Electronic Circuits

[Envelope detector

1. Diode envelope detector

[1] https://www.electronics-notes.com/articles/radio/modulation/am-diode-detector-demodulator.php

- Simplest form of AM demodulation

- Used in early days of radios

- Modern form: IC with inbuilt detectors

- Still used in RF signal level detection

- Not as good as other types of the envelope detector: more distortions

1) Basic form

Figure: Transformer-coupled diode envelope detector. A DC return path is provided by the transformer secondary winding.

- Diode: use Schottky diodes with lower turn-on voltage (0.2V)

- LPF: τ_c << τ << τ_m

- Input impedance: R(diode, forward) + R || C1, usually small so that impedance matching is required.

- Output impedance: high (find?)

Figure: Transformer-coupled diode envelope detector. An input resistor provides the DC return path, which also affects input impedance of the envelope detector.

Keywords:

Diode envelope detector, sensitivity

--, input impedance

--, output impedance

--, impedance matching

--, RF

--, wideband

--, low frequency

[2] Transistor envelope detector

https://www.edn.com/am-detector-more-sensitive-than-simple-diode/

Figure: Traditional AM detector. Input

Figure: Improved AM detector. Input impedance = 300 k, Oputput impedance = low, 100% modulation = OK

Figure: Improved AM detector with AGC output.

Keywords:

Envelope detector with AGC

Transistor envelope detector

Envelope detector, high modulation index

[3] Sensitive envelope detector with transistor

http://zpostbox.ru/sensitive_envelope_detector_with_transistor.html

Diode/transistor envelope detector sensitivity: low when Vin < 0.1V

Op-amp envelope detector: sensivity 1mV, high dynamic range

Figure: Sensitive TR envelope detector. 3mV input with 80% modulation, 180mV output

Figure: Sensitive TR envelope detector. 1.5mV input with 80% modulation, 180mV output

[3] AM demodulation

https://www-elec.inaoep.mx/~rogerio/DemodulationGeneral.pdf

Also called the sereis- (voltage-) diode detector