Square Law Demodulator -

# Square Law Demodulator

In each positive half-cycle of the input, the demodulating diode is polarized forward and charges the connected filter capacitor C via the load resistor R to almost the maximum value of the input voltage. The block diagram of the quadratic distribution demodulator is shown in Fig. 2. Of these terms, the only desired term bEc2 is mx(t), which is due to the term b v12. Therefore, the name of this demodulator is quadratic demodulator. This demodulator contains a quadratic distribution and a low-pass filter. The AM wave \$V_1left ( t right )\$ is applied as input to this demodulator. The envelope demodulator consists of a diode and an RC filter. The standard AM wave is applied to the input of the demodulator. We try to extract the signal from the AM signal message using a square demodulator. | M(t)| \$ leq 1.0\$, so for analog signals \${m^2(t)}\$ will be small most of the time.

Also \$k_a < 1.0\$, so \${k_a}^2 ll 1.0\$. You can usually ignore the term. If you can`t, use something other than a quadratic distribution demodulator. The input-output characteristics, i.e. the transmission characteristics of a quadratic distribution demodulator, are nonlinear and are mathematically expressed as follows: The process of extracting an original message signal from the modulated wave is called detection or demodulation. The circuit that demodulates the modulated shaft is called a demodulator. The following demodulators (detectors) are used to demodulate the AM wave. The envelope demodulator is a simple and highly efficient device suitable for detecting a narrowband AM signal. An envelope demodulator produces an output signal that closely follows the envelope of the input AM signal. It is used in all commercial AM radio receivers.

There are two types of AM detectors or demodulators such as: The input-output waveforms for the envelope demodulator are shown in Fig. 4. Here we assumed that the diode is ideal and that the AM wave applied to the input of the demodulator is provided by an internal resistance source Rs. We know that the mathematical relationship between input and output of the quadratic law device We need to select the values of the components so that the capacitor charges very quickly and discharges very slowly. As a result, we get the voltage waveform of the capacitor, which corresponds to the envelope of the AM wave, which is almost similar to the modulating signal. The capacitor is now discharged by R between the positive peaks, as shown in Fig. 4. The unloading process continues until the next positive half-cycle. Negative peak clipping occurs as a result of this overmodulation, as shown in Fig.

6. The ratio between the desired signal and the unwanted signal is given by: The AM wave \$sleft ( t right )\$ is applied as input to this detector. The envelope detector is used to detect (demodulate) AM waves at a high level. Here is the block diagram of the envelope detector. where v1(t) = detector input voltage = AM wave If the input signal becomes higher than the capacitor voltage, the diode redirects and the process repeats. The charging time constant RsC must be short compared to the carrier period 1/fc. On the other hand, the discharge time constant RC must be long enough for the capacitor to discharge slowly through the charge resistor R. However, this time constant must not be too long so that the voltage of the capacitor cannot discharge with the maximum rate of change of the envelope. As soon as the capacitor is charged to the peak value, the diode stops conducting.

This distortion occurs because the modulation index on the detector output side is higher than on the input side. Therefore, at a higher modulation depth of the transmitted signal, overmodulation can occur at the detector output. A narrowband AM wave is one where the carrier frequency fc is much higher relative to the bandwidth of the modulating signal. This envelope detector consists of a diode and a low-pass filter. Here, the diode is the main sensing element. Therefore, the envelope detector is also called a diode detector. The low-pass filter contains a parallel combination of resistor and capacitor. This ratio should be maximized to minimize distortion. To achieve this, we must choose |mx(t)| low from unit (1) for all values of t. If m is small, then the AM wave is weak.

This means that the distortion in the detector output is only low if the AM applied is low and the modulation percentage is very low. \$frac{K_2{A_{c}}^{2}}{2} cos left ( 4 pi f_ct right )+frac{k_2 {A_{c}}^{2}{k_{a}}^{2}m^2left ( t right )}{2}+frac{k_2 {A_{c}}^{2}{k_{a}}^{2}m^2left ( t right )}{2} cosleft ( 4 pi f_ct right )+\$ The capacitor is charged by D and Rs, when the diode i is lit and discharges by R when the diode is off.