RF receiver circuit and RF transmitter circuit

Posted Date: 2023-07-14

“With a view to higher grasp the working precept of the smartphone RF circuit, on this article, we analyze the RF receiving circuit, the RF transmitting circuit, and the frequency synthesizer circuit in accordance with the circuit construction of the cell phone. The RF circuit has a vital guiding significance.

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With a view to higher grasp the working precept of the smartphone RF circuit, on this article, we analyze the RF receiving circuit, the RF transmitting circuit, and the frequency synthesizer circuit in accordance with the circuit construction of the cell phone. The RF circuit has a vital guiding significance.

RF receiver circuit

The cell phone radio frequency receiving circuit primarily completes the filtering, frequency mixing demodulation, decoding and different processing of the obtained radio frequency sign, and eventually restores the sound sign.

1. RF receiving sign course of

The wi-fi sign obtained by the antenna is filtered by the antenna matching circuit and the receiving filter circuit, after which amplified by the low noise amplifier (LNA). The voltage-controlled oscillating sign is blended to acquire the obtained intermediate frequency sign. After the intermediate frequency amplification, quadrature demodulation is carried out within the demodulator to acquire the obtained baseband (RX I/Q) sign.

The obtained baseband sign is demodulated by GMSK within the baseband circuit, deinterleaved, decrypted, channel decoded, and so on., after which PCM decoded to revive it to an analog voice sign, push the receiver, and you'll hear the voice of the opposite get together.

2. Block diagram of the RF receiving circuit

Cell phone receivers have three fundamental body constructions: superheterodyne receivers, zero-IF receivers, and low-IF receivers.

(1) Superheterodyne receiver

For the reason that sign obtained by the antenna may be very weak, and the enter sign degree required by the frequency discriminator is excessive and must be steady, the overall acquire of the amplifier usually must be above 120dB. In truth, it's troublesome to attain; as well as, the passband width of the high-frequency frequency selective amplifier is simply too vast, when the frequency modifications, all of the tuning loops of the multi-stage amplifier should be modified, and it's troublesome to attain unified tuning. of.

The superheterodyne receiver doesn't have this drawback. It converts the obtained RF sign into a hard and fast IF, and its predominant acquire comes from a steady IF amplifier.

①Superheterodyne main mixing receiver

There is just one mixing circuit within the radio frequency circuit of the superheterodyne main mixing receiver. The schematic block diagram of the superheterodyne main mixing receiver is proven in Determine 6-5.

RF receiver circuit and RF transmitter circuit
Determine 6-5 Precept block diagram of superheterodyne main mixing receiver

②Superheterodyne secondary mixing receiver

There are two mixing circuits within the radio frequency circuit of the superheterodyne secondary mixing receiver. The schematic block diagram of the superheterodyne secondary mixing receiver is proven in Determine 6-6.

RF receiver circuit and RF transmitter circuit
Determine 6-6 Precept block diagram of superheterodyne secondary mixing receiver

In contrast with the first mixing receiver, the secondary mixing receiver has another mixer and one VCO, which is known as IFVCO or VHFVCO in some circuits. In such a receiver circuit, if the RX I/Q demodulation is phase-locked demodulation, the reference sign used for demodulation often comes from the reference frequency sign.

(2) Zero IF receiver

The zero-IF receiver will be stated to be essentially the most built-in receiver. Because of its small dimension and low value, it's the most generally used receiver in present good telephones.

The precept block diagram of the zero-IF receiver is proven in Determine 6-7.

RF receiver circuit and RF transmitter circuit
Determine 6-7 Precept block diagram of zero-IF receiver

The zero-IF receiver doesn't have an IF circuit and immediately demodulates the I/Q sign, so there's solely a modulation and demodulation provider sign oscillator (SHF VCO) shared by the transceiver, and its oscillation frequency is immediately used for transmit modulation and obtain demodulation (obtain, transmit and obtain). completely different oscillation frequencies).

(3) Low-IF receiver

The low-IF receiver, also referred to as the near-zero-IF receiver, has the same benefits of the zero-IF receiver, and on the identical time avoids the issue of low-frequency noise brought on by the DC offset of the zero-IF receiver.

The circuit construction of the low-IF receiver is considerably much like the super-heterodyne main mixing receiver. The schematic block diagram of the low-IF receiver is proven in Determine 6-8.

RF receiver circuit and RF transmitter circuit
Determine 6-8 Precept block diagram of low-IF receiver

RF transmitter circuit

The radio frequency transmitting circuit of the cell phone primarily completes the modulation, transmission transformation, energy amplification of the transmitted radio frequency sign, and transmits it by means of the antenna.

1. RF transmission sign course of

The microphone converts the sound into an analog electrical sign, which is encoded by PCM, after which transformed right into a digital sign, which is processed by a logic audio circuit for digital voice processing, that's, voice coding, channel coding, interleaving, encryption, burst formation, TX I// Q separation.

The separated four-way TX I/Q alerts are despatched to the transmitting IF circuit to finish the I/Q modulation. section) to acquire a pulsating DC sign containing the transmitted information to regulate the output frequency of the transmitting native oscillator, as the ultimate sign, after energy amplification, it's transmitted from the antenna.

2. Block diagram of the RF transmitter circuit

There are three fundamental body constructions of cell phone radio frequency transmitting circuit: one is the radio frequency transmitting circuit with the transmitting conversion circuit; the opposite is the radio frequency transmitting circuit with the transmitting up-conversion circuit; the third is the direct modulation radio frequency transmitting circuit.