summarize

radio-frequency technologyA technology that is essential in the Internet of Things and our lives, since the emission of radio waves requires a transmitter, an electronic device that is used to generate radio waves in order to transmit or send data with the help of an antenna. Transmitters are capable of generating radio frequency alternating current, which is then applied to an antenna, which in turn radiates it in the form of radio waves. There are many types of transmitters depending on the standards and types of devices used; for example, many modern devices with communication capabilities have transmitters such as Wi-Fi, Bluetooth, NFC, and cellular.

RF modulation

If just send a radio frequency signal is meaningless, need in the process of transmitting the information will be released, so that in the receiving end can be demodulated to receive the information down, so as to achieve the purpose of information interoperability.

Why not just use the input signal directly? So why not just use it directly? Why do you need carriers and modulation?

This is because very low frequency electromagnetic waves can carry the input signal (without a carrier). However, the problem is that this would require considerable amplification to transmit those very low frequencies. The input signal itself is not very powerful and would require a fairly large antenna to transmit the information. To keep communications cheap and easy, and to require less power to carry as much information as possible, carrier systems with modulated carriers are used.

Analog signals - digital signals

RF modulation is subdivided into two broad categories: analog modulation and digital modulation.

1. Analog modulation receives analog signals while digital modulation receives digital signals.
2. Analog modulation is cheaper to implement than digital modulation.
3. Analog modulation has one RMS range, while digital modulation has only two.
4. Digital modulation produces a more accurate output than analog modulation.

RF modulation

• Amplitude modulation (AM) causes the baseband signal to change the amplitude or height of the carrier to create the desired information content.
• Amplitude modulation (AM) causes the baseband signal to change the amplitude or height of the carrier to create the desired information content.
• Frequency Modulation (FM) causes the instantaneous frequency of a sine wave carrier to deviate from the center frequency by an amount proportional to the instantaneous value of the modulating signal.
• Amplitude shift keying (ASK) transmits data by changing the amplitude of the transmitted signal.
• Frequency shift keying (FSK) is a digital modulation scheme that uses two or more output frequencies.
• Phase-shift keying (PSK ) is a digital modulation scheme in which the phase of the transmitted signal varies according to the baseband data signal.

RF Name Explanation

RF Filter (RF Filter)

Filters are essential to filter out unwanted signals entering the radio spectrum. They can be used in conjunction with a variety of electronic devices; however, its most important use is in the field of radio frequency.RF filters filter out noise or reduce interference from external signals that may affect the quality or performance of any communication system. A low-pass filter (LPF) allows frequencies below a specific frequency to pass; a high-pass filter (HPF) allows frequencies above a specific frequency to pass; a band-pass filter (BPF) allows frequencies between two frequencies to pass; and a band-stop filter (NOT) refuses to allow frequencies between two frequencies to pass and allows all other frequencies to pass at the same time. A simple example is shown below.

RF Mixer (Mixer)

RF mixer devices are used in RF transceiver upconversion and downconversion modules. A mixer is used to change the frequency of an electromagnetic signal while retaining all other characteristics of the initial signal (e.g., phase and amplitude).An RF mixer is a three-port device. The three ports are usually denoted as radio frequency (RF), intermediate frequency (IF), and local oscillator (LO).The RF and IF ports are bidirectional.

The RF mixer has 3 ports RF, IF and LO. it has two input ports and one output port.
For upconversion, IF and LO = input; RF = output.
For downconversion, RF and LO = input; IF = output.

Note: Mixing these two frequencies produces a useless signal called a mirror frequency. Therefore, the bandpass filter needs to be placed before and after the mixer.

Power Amplifier

Two common examples of converting low-power signals into high-power signals are audio amplifiers, which are used to drive speakers and headphones, and RF power amplifiers, such as those used in the final stages of transmitters. Therefore power amplifiers are also needed inside RF to increase the power of a signal.

An amplifier is a device that turns a small input signal (energy) into a large output signal (energy). This means that the amplifier provides a lot of energy to the input signal. So where does the amplifier get its energy from? It is supplied by an external energy source, labeled "Vdd", as shown below. In the case of your cell phone, this Vdd is connected to the battery, and in the case of a base station in a large system, this part will eventually be connected to the external power cord.

Related resources

• Electronic training materials
• microwave technology
• RF Knowledge
• Knowledge Sharing