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Project 7: AM Receivers
Published in Thad B. Welch, Cameron H.G. Wright, Michael G. Morrow, ® to C with the TMS320C6x DSPs, 2016
Thad B. Welch, Cameron H.G. Wright, Michael G. Morrow
One of the most inexpensive AM demodulation techniques employs the envelope detector. Traditional circuit-based implementations of the envelope detector utilize a diode and an analog lowpass (LP) filter to demodulate the AM signal. The diode halfwave rectifies the incoming signal; that is, it passes either the positive half of the AM signal or the negative half of the AM signal, depending upon how the diode is connected in the circuit. The analog LP filter extracts the relatively low frequency message from the AM signal’s envelope. The effect of halfwave rectification can be seen in Figure 16.3 (time domain) and Figure 16.4 (frequency domain), where an ideal diode is assumed to pass only the positive half of the AM signal. The nonlinear action of the diode has caused other frequency components to appear in the signal, as is evident in Figure 16.4.
Making Sounds with Digital Electronics
Published in Russ Martin, Sound Synthesis and Sampling, 2012
Extracting the envelope from a sample sound is relatively straightforward in comparison to pitch extraction. The sample sound is low-pass filtered, and then a ‘leaky’ peak detector is used to produce a simple curve that approximates to the original volume envelope. The setting of the low-pass filtering and the peak detector decay time constant govern the effectiveness of the envelope detection. The low-pass filter should be set so that its cut-off frequency is lower than the lowest expected frequency in the input sample, but setting it too low can slow down the response of the envelope, resulting in slow attack, decay or release times.
Continuous-Time Circuits
Published in Tertulien Ndjountche, CMOS Analog Integrated Circuits, 2017
An envelope detector can also be implemented using a full-wave rectifier followed by a lowpass RC filter. Figure 7.100(a) shows the circuit diagram of a rectifier [60]. Due to the high gain of the amplifier, the voltage at the inverting and noninverting nodes should be made equal. This is achieved when a rectified version of the input signal is reproduced at the gate of T3 or output. The rectifier shown in Figure 7.100(b) [63] is based on a comparator. Each of the transistors T1 and T2, which operate as a switch, is closed or open according to the input signal polarity.
Test strategy for a 25-dBm 1-GHz CMOS power amplifier in a wireless power transfer context
Published in International Journal of Electronics, 2021
Fabian L. Cabrera, F. Rangel de Sousa
The topology of the envelope detector is shown in Figure 3(a). The amplitude of the sensed signal is reduced with a capacitive divider to not exceed the nominal voltage of the transistors (1.8 V). A full-wave rectifier (Mandal & Sarpeshkar, 2007) is used as an envelope detector. This rectifier does not require additional biasing circuits which is advantageous when compared with small-signal peak detectors (Bhagavatula et al., 2013). A capacitor filters out the ac components. An amplifier configured as voltage-follower is used to buffer the dc voltage, so it can be measured externally. The characteristic curve relating the output dc voltage () with the peak voltage () of each node V+ and V– is shown in Figure 3(b). The curve is approximately linear for values above 1.5 V, below this value the response is less sensitive because the voltages at the gates of the transistors are lower than the threshold voltages. The amplifier was implemented with two differential pairs as shown in the schematic of Figure 3(c). The differential pairs are complementary (NMOS and PMOS) to achieve rail-to-rail operation. The bias voltages and are obtained from current mirrors with a reference current of 10 A.