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university:courses:electronics:electronics_lab_diode_ring_modulator [20 Mar 2019 13:28] – Hannah Rosete | university:courses:electronics:electronics_lab_diode_ring_modulator [07 Feb 2022 15:11] (current) – [Diode Ring Modulator] Doug Mercer | ||
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- | ====== Diode Ring Modulator ====== | + | ======Activity: |
===== Objective ===== | ===== Objective ===== | ||
+ | The objective of this activity is to describe the operation of a diode ring mixer, to identify some of its applications, | ||
===== Materials ===== | ===== Materials ===== | ||
+ | ADALM2000 Active Learning Module\\ | ||
+ | Solder-less breadboard\\ | ||
+ | 4 - 100Ω Resistors\\ | ||
+ | 2 – 1kΩ Resistors\\ | ||
+ | 4 – 1N914 Diodes\\ | ||
+ | 2 - Two-triflar-winding Transformers (if available)\\ | ||
===== Background ===== | ===== Background ===== | ||
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One of the most prevalent balanced modulators is the Diode Ring Modulator, otherwise known as Lattice Modulator. It comprises of four diodes originally fashioned as a “ring”, thus the moniker, and input and output transformers. The modulator has two inputs: a single frequency carrier and a modulating signal, which can be a single frequency or a complex waveform. The carrier is applied at the center taps of the input and output transformers and the modulating signal at the primary of the input transformer. The output, however, is measured at the secondary of the output transformer. Figure 1 shows the diode ring modulator in two different circuit orientations. | One of the most prevalent balanced modulators is the Diode Ring Modulator, otherwise known as Lattice Modulator. It comprises of four diodes originally fashioned as a “ring”, thus the moniker, and input and output transformers. The modulator has two inputs: a single frequency carrier and a modulating signal, which can be a single frequency or a complex waveform. The carrier is applied at the center taps of the input and output transformers and the modulating signal at the primary of the input transformer. The output, however, is measured at the secondary of the output transformer. Figure 1 shows the diode ring modulator in two different circuit orientations. | ||
- | {{ : | + | {{ : |
- | <WRAP centeralign> | + | <WRAP centeralign> |
Also, the diode ring modulator is one of the most extensively used circuits in electronic communications. In addition to producing DSBSC signals, it is also used in frequency and phase modulation systems as well as in digital modulation systems, such as PSK and QAM. | Also, the diode ring modulator is one of the most extensively used circuits in electronic communications. In addition to producing DSBSC signals, it is also used in frequency and phase modulation systems as well as in digital modulation systems, such as PSK and QAM. | ||
- | The orientation of the diodes in a ring modulator must not be mistaken with that of a diode bridge rectifier. They may take the similar “ring” shape; however, the ring modulator has all its diodes face either clockwise or counterclockwise while the bridge rectifier has its diodes facing either left or right. | + | The orientation of the diodes in a ring modulator must not be mistaken with that of a diode bridge rectifier. They may take the similar “ring” shape; however, the ring modulator has all its diodes face either clockwise or counterclockwise while the bridge rectifier has its diodes facing either left or right.\\ |
===== Operation ===== | ===== Operation ===== | ||
- | The diodes used in a diode ring modulator can either be silicon, silicon Schottky-barrier or gallium-arsenide. They serve as switches that control whether the input signal is passed with or without a 180° phase reversal. The carrier signal is the one that sets the diodes on and off at a high rate of speed. It is important to know that for the modulator to operate, the carrier’s amplitude must be adequately greater than the modulating signal’s, about six to seven times greater. | + | The diodes used in the diode ring modulator can either be silicon, silicon Schottky-barrier or gallium-arsenide. They serve as switches that control whether the input signal is passed with or without a 180° phase reversal. The carrier signal is the one that sets the diodes on and off at a high rate of speed. It is important to know that for the modulator to operate, the carrier’s amplitude must be adequately greater than the modulating signal’s, about six to seven times greater. |
- | During the positive half-cycle, D1 and D2 are forward biased and on, and D3 and D4 are reverse biased and act as open circuits. | + | \\ {{ : |
+ | <WRAP centeralign> | ||
- | {{ : | + | During the positive half-cycle, D1 and D2 are forward biased and on, and D3 and D4 are reverse biased and act as open circuits. The carrier current is then equally divided at the center tap of the input transformer’s secondary and flows in opposite directions through the upper and lower halves of the winding. The currents in the upper and lower parts each produce a magnetic field that is both equal and opposite with each other therefore, the magnetic fields produced cancel out and the carrier is suppressed. Thus, the modulating signal is passed from the input to the output transformers through D1 and D2 without phase reversal. Figure 2 shows the positive half-cycle |
- | <WRAP centeralign> | + | |
- | {{ : | + | \\ {{ : |
- | <WRAP centeralign> | + | <WRAP centeralign> |
+ | Figure 3 illustrates the negative half-cycle operation of the diode ring modulator. Diodes D1 and D2 are reversed biased and off while D3 and D4 are forward biased and on. Again, the same thing happens to the carrier current. It splits equally in the primary of the output transformer and both current produce magnetic fields equal and opposite with one another. | ||
+ | The figure below shows the waveforms of the diode ring modulator in a timing diagram. | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | |||
+ | The output waveform of the diode ring modulator has the carrier signal suppressed and is made up of the sum and difference of the input frequencies. They are RF pulses that takes the shape and amplitude of the modulating signal at the rate of the carrier signal. Ideally, the carrier signal is totally suppressed, however, this doesn’t really happen. A small carrier component always goes with the output signal and this is called a **//carrier leak//**. This happens for a few reasons: First, if the transformers are not exactly center tapped; and second, if the diodes are not perfectly matched. | ||
+ | |||
+ | ===== Hardware Setup ===== | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | |||
+ | Construct the circuitry shown in Figure 5 on a solderless breadboard. Use the 1N914 fast switching diode for the diode ring. Set W1 as a 1kHz sine modulating signal with 1V amplitude peak-to-peak and set W2 as a 10kHz sine carrier with a 3V amplitude peak-to-peak. For the input and output transformers, | ||
+ | |||
+ | ===== Procedure ===== | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | Observe the output waveform of the circuit. It should have a similar waveform shown in the simulated waveform above. | ||
+ | |||
+ | ===== Questions ===== | ||
+ | 1. Change the turns ratio of both the input and output transformers. Observe and compare the output waveforms. \\ | ||
+ | 2. Interchange the position of W1 and W2 in the circuit. Compare it with the original output waveform. What happens to the output waveform? | ||
+ | |||
+ | ====== Simplified Diode Ring Modulator ====== | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | |||
+ | By taking out the transformers, | ||
+ | |||
+ | ===== Hardware Setup ===== | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | |||
+ | These transformerless version of the diode ring modulator can be easily supplied with the sum of the carrier and modulating signals at one junction and the difference of the signals at other using the ADALM2000’s signal generators. Set up the breadboard with the output of the first waveform generator, W1, to the other end of R1, and the second waveform generator, W2, at the other end of R2. Connect scope input 1+ in the junction of D1, D3, and R4. Attach scope input 1- to the node that links D2, D4, and R3. Finally, connect the node between R3 and R4 to ground. See Figure 8 for connections. | ||
+ | |||
+ | ===== Procedure ===== | ||
+ | In this activity, we will utilize a carrier with a waveform equation of // | ||
+ | |||
+ | <WRAP centeralign>< | ||
+ | <WRAP centeralign>< | ||
+ | |||
+ | where: | ||
+ | * f< | ||
+ | * f< | ||
+ | |||
+ | In this simplified approach, we will directly feed the sidebands to the inputs. Taking note of the carrier and the modulating signals, we will have //f(t) = 3sin(10kt) + 0.5sin(1kt)// | ||
+ | |||
+ | In the signal generator, set the equation //f(t) = (3*sin(10*t)) + (0.5*sin(t))// | ||
+ | |||
+ | \\ {{ : | ||
+ | <WRAP centeralign> | ||
+ | |||
+ | |||
+ | ===== Question ===== | ||
+ | 1. What happens if the resistor values of Figure 7 are changed? Change R1 and R2 with 1 kΩ resistors, what happens to the amplitude of the output waveform? Revert back R1 and R2 to their previous values. | ||
+ | \\ | ||
+ | \\ | ||
+ | <WRAP round download> | ||
+ | **Lab Resources: | ||
+ | * Fritzing files: [[downgit> | ||
+ | * LTspice files: [[downgit> | ||
+ | </ | ||
+ | |||
+ | ====== Further Reading ====== | ||
+ | |||
+ | Some additional resources: | ||
+ | * [[adi> | ||
+ | * [[http:// | ||
+ | * [[https:// | ||
+ | * [[https:// | ||
+ | |||
+ | **Return to Lab Activity [[university: | ||