Which diode is used in am detector circuit

Enable markers 1 and 2 from the Markers tab and the Marker Table. A plot example is presented in Figure 6. Set the Sweep range from 9 kHz to 11kHz. Set the Sweep range from 20Hz to Hz. In Figure 8, the main peak is at the Hz message frequency. Since the frequency analysis is made on the output signal using a basic envelope detector circuit, we are able to see both the message and carrier signal.

In contrast to the applied input signal, where the carrier amplitude is larger than the message amplitude, on the spectrum analyzer plot we can notice that, in terms of magnitude, the message signal Hz is emphasized with respect to the carrier signal see Marker table. A similar circuit is added to the circuit in Figure 1 , the only difference being that the diode is reversed, allowing the negative voltages to pass through the RC circuit.

The generated waveform is presented in Figure Disconnect the capacitors C1 and C2 from the circuit and observe the output signal. A plot example is presented in Figure Without the capacitors connected, the circuit works like a positive half-wave rectifier and negative half-wave rectifier, separating the positive half from the negative one.

The obtained signal is the envelope of the positive half wave and negative half wave obtained previously. Which are the drawbacks in this case? For the circuit in Figure 1, if a resistor is added in series with the diode, between D1 and R1, how is the output affected? Explain the differences. The simple diode based envelope detector of Figure 1 does not well or at all if the amplitude i. Swing is less than the forward turn voltage of the diode.

A way around this limitation is to introduce a small DC bias to the diode. This small bias current moves to quiescent operating point of the circuit to right at the turn on point of the diode.

The base current of Q1 flows in diode D1 forward biasing it. During the positive half cycles of the modulated input D1 turns off and the input signal peaks charge filter capacitor C2. During the negative half cycles of the input signal transistor Q1 turns off and D1 turns on harder supplying the input current. To test this circuit first use the same modulated signal you used in the simple diode envelope detector example.

Compare the new design to the simple diode envelope detector. A plot example of the input and output waveforms for the biased envelope detector is presented in Figure Return to Lab Activity Table of Contents.

Analog Devices Wiki. It is worth noting in this circuit that the secondary of the transformer provides a DC return to ground. Sometimes when the AM signal detector is used using a capacitor connection tot he previous stage, then a resistor or choke inductor to ground must be used at the input so that a DC return path is provided.

If not the circuit will not operate correctly. The value of the resistor on the input providing the DC return path is normally critical, but it can help provide the require match without absorbing too much signal.

In rectifying the RF signal, the AM diode detector provides an output equivalent to the envelope of one half of the signal, i. In view of the operation of the diode detector, it may sometimes be referred to as an envelope detector. The incoming amplitude modulated RF signal consists of a waveform of both positive and negative going voltages as shown. Any audio transducer would not respond to this. The diode envelope detector rectifies the waveform leaving only the positive or negative half of the waveform.

Swing is less than the forward turn voltage of the diode. A way around this limitation is to introduce a small DC bias to the diode. This small bias current moves to quiescent operating point of the circuit to right at the turn on point of the diode.

On your solder-less breadboard construct the biased envelope detector circuit as shown in Figure 8. Absent any modulated input the DC quiescent operating point seen at the emitter of Q 1 will be the voltage at the junction of R 1 and R 2 minus the diode drop of D 1 and the V BE of Q 1.

The base current of Q 1 flows in diode D 1 forward biasing it. During the positive half cycles of the modulated input D 1 turns off and the input signal peaks charge filter capacitor C 2. During the negative half cycles of the input signal transistor Q 1 turns off and D 1 turns on harder supplying the input current.

To test this circuit first use the same modulated signal you used in the simple diode envelope detector example. Compare the new design to the simple diode envelope detector. Analog Devices Wiki. Analog Devices Wiki Resources and Tools. Quick Start Guides. Linux Software Drivers. Microcontroller Software Drivers. ACE Software. Technical Guides. Education Content. University Program Overview. Teaching and Lab Materials. Wiki Help. About Wiki. This version 03 Jan was approved by Robin Getz.