Q.Draw the block diagram of a 2G cell phone system and briefly describe the function of each block.

A 2G cell phone is organised into an RF section, a baseband section and an embedded control section, and its block diagram shows how voice is converted, processed and radiated.

[!ANSWER]

The 2G cell phone has three main parts: the RF section (transmitter and receiver with mixers, a frequency synthesiser/local oscillator, a low-noise amplifier and a power amplifier) that handles the radio signal to and from the antenna; the baseband section (a vocoder with A/D and D/A converters and a Digital Signal Processor) that converts and compresses voice and does modulation/demodulation and filtering; and the embedded controller (a fast 32-bit microprocessor with RAM, ROM and flash) that handles all digital control, signalling, hand-offs and the user functions (display, keyboard, dialling, caller ID).

[!TLDR]

A 2G phone = RF section (radio front-end), baseband section (vocoder + DSP + converters) and an embedded controller (control, signalling and user functions).

The block diagram of a basic 2G cell phone system is divided into three sections — RF, Baseband and Control — connected between the antenna and the user.

1. RF section: This contains the transmitter and receiver circuits. On the receive side, the antenna signal passes through the antenna switch/duplexer to a Low Noise Amplifier (LNA) and then to a mixer, which uses a frequency synthesiser (local oscillator) to select the channel. On the transmit side, the outgoing signal is up-converted by a mixer and boosted by a Power Amplifier before going to the antenna. The frequency synthesiser feeds both mixers for channel selection.

2. Baseband section: This contains the vocoder together with its A/D converter and D/A converter, plus a Digital Signal Processor (DSP) chip. A vocoder is a circuit that converts voice into digital format and compresses the digital data. The DSP handles baseband and intermediate-frequency filtering, modulation, demodulation and mixing. On receive, the signal is digitised (A/D), processed by the DSP and vocoder and sent to the speaker; on transmit, the microphone signal is coded by the vocoder and DSP and converted back to analog (D/A) for the RF section.

3. Embedded controller (Control section): This handles all the digital control and signalling — hand-offs, connection and identification operations — transparently to the subscriber. It also runs the display, keyboard and user functions such as number storage, auto-dialling and caller ID. It is usually a very fast 32-bit microprocessor with considerable RAM, ROM and flash memory. Additional power-saving circuitry is included to give longer battery life.

[!ANSWER]

The 2G cell phone block diagram has an RF section (antenna switch/duplexer, LNA, mixers, frequency synthesiser and power amplifier) that handles the radio signal; a baseband section (vocoder with A/D and D/A converters and a DSP) that digitises, compresses and processes voice and performs modulation/demodulation and filtering; and an embedded controller (a fast 32-bit microprocessor with RAM, ROM and flash) that manages all digital control, signalling, hand-offs and user functions such as the display, keyboard, dialling and caller ID.