| IEEE 802.11b/g RF Transceiver (2.4GHz) |
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General Description |
The RTL8225/RTL8225-VF is a fully integrated RF transceiver compliant with IEEE Wireless LAN standards 802.11b, and 802.11g. When used with a baseband/MAC processor (e.g. RTL8185 or RTL8187) and a 2.4GHz power amplifier, it forms a complete solution for the 2.4GHz ISM band. The RTL8225/RTL8225-VF uses a direct conversion/zero-IF architecture to limit the number of required active blocks and avoid external, cumbersome, IF bandpass SAW filters for channel selection.
The receive path includes sets of single-ended Low Noise Amplifiers (LNA), followed by RF-to-baseband I/Q demodulators, baseband filters, and discrete-step variable-gain amplifiers. The entire receive chain provides linear and monotonic automatic gain control, RSSI signal, and fast DC offset cancellation mechanisms to a baseband processor.
The transmitter path includes integrated reconstruction filters, discrete-step variable-gain amplifiers, a baseband-to-RF I/Q modulator, and pre amplifiers. A linear and monotonic gain control is distributed throughout the transmitter chain to ensure high linearity as well as to simplify Automatic Gain Control (AGC).
The modulator and demodulator are driven by an internal Voltage Controlled Oscillator (VCO). The VCO is phase-locked by an internal 3-wire-interfaced PLL. In the RTL8225-VF, a crystal oscillator using an external crystal and two Low Drop-Out (LDO) regulators are also integrated.
The differences between the RTL8225 and RTL8225-VF are:
- The RTL8225 needs two external LDO regulators. These LDOs are integrated into the RTL8225-VF.
- The RTL8225 uses an external oscillator to generate a 40MHz clock source as input to the RTL8225. The RTL8225-VF replaces the oscillator with crystal.
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Features
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- Fully complies with IEEE 802.11 b/g specifications
- Single-chip zero-IF transceiver
- Rx: VGA gain control range is 60dB in 1dB steps. Total gain control range is 90dB
- Tx: VGA gain control range is 6dB in 1dB steps. Total gain control range is 36dB
- Integrated channel-selection filters, reconstruction filters, VCO, and synthesizers
- In the RTL8225-VF, integrated Low Drop-Out regulators
- High-speed 3-wire serial interface
- 0.18µm CMOS process
- 48-pin 7x7mm QFN package
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Applications
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- CardBus PC Card
- PCI, PCI Express, and MiniPCI Boards
- Wireless USB Adapter and Mini-Card
- Access Point
- Network Interface Card
- IEEE 802.11 b/g Transceiver
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