RTC6705A

Introduction

The RTC6705A is a high-performance, single-chip 5.8 GHz FM Transmitter launched by RichWave Technology Corporation (Taiwan). Designed specifically for IEEE 802.11a and 5.8 GHz ISM band analog wireless transmission, it is widely used in scenarios requiring analog audio/video signal transmission. It integrates an RF modulator, Voltage-Controlled Oscillator (VCO), Phase-Locked Loop (PLL), and Power Amplifier (PA), allowing a complete wireless transmission system to be built with minimal external components.

Important Note: Despite the "RTC" prefix, in the electronic components market, RTC6705A refers to an RF Transmitter chip, not a Real-Time Clock chip. When purchasing, please verify the "RF Transmitter" or "Video Transmitter" description in the datasheet to avoid confusion.

Key Features

RF & Modulation Performance

• Operating Frequency: 5.725 GHz ~ 5.875 GHz (covers the full 5.8 GHz ISM band).
• High Output Power: Built-in power amplifier with a typical output power of +13 dBm (approx. 20 mW), configurable via pins down to +2 dBm to meet regulatory requirements in different regions (e.g., CE/FCC).
• High Gain: Typical gain up to 32 dB, allowing full power output without an external driver amplifier.
• Modulation: Supports Wideband Frequency Modulation (FM), suitable for analog video and audio signal transmission.
• Linearity: EVM (Error Vector Magnitude) is only 3% for 64QAM modulation at 26 dBm output, ensuring high signal quality.

Integrated Functions

• Dual Audio Subcarriers: Built-in two independent audio modulators supporting 6.0 MHz and 6.5 MHz subcarrier frequencies for stereo or dual-channel audio transmission.
• Frequency Synthesizer: Integrated VCO and PLL-based frequency synthesizer ensures frequency stability.
• Smart Control:
  • SPI Interface: Allows programming of internal registers via a microcontroller to precisely adjust the transmission frequency.
  • Fixed Channel Mode: 24 fixed channels can be selected directly via dedicated digital pins (6 pins) without an external MCU, greatly simplifying design.
• Harmonic Suppression: Built-in 3.8 GHz notch filter effectively suppresses second harmonics, simplifying external filter circuits.

Package & Reliability

• Package: 40-pin QFN (Quad Flat No-Lead) package, compact size (typical dimensions approx. 6mm x 6mm or 8.4mm x 6.4mm depending on batch), RoHS lead-free compliant.
• Supply Voltage: 3.3V single power supply.
• Operating Temperature: Industrial grade range, typically -40°C to +85°C or -10°C to +90°C (depending on datasheet version).

Typical Specification Table

Typical Applications

• 5.8 GHz Analog Video Transmission Systems:
  • Wireless Security: Wireless CCTV cameras, home security systems.
  • Consumer Electronics: Baby monitors, wireless doorbells, wireless headphones, wireless microphones.
  • Drones (FPV): Entry-level or low-cost analog FPV video transmission systems (Note: Modern digital systems often use COFDM).
  • Automotive: Wireless reverse cameras, in-car entertainment wireless transmission.
  • Industrial Control: Wireless video surveillance backhaul, industrial field data acquisition.

Development & Design Notes

1. Peripheral Circuit Design: Although highly integrated, the chip requires a peripheral matching network (Match Network) to optimize power transfer to the antenna and harmonic suppression. Reference designs typically include a combination of inductors, capacitors, and resistors.
2. Antenna Design: A 50-ohm impedance PCB onboard antenna or external rod antenna is recommended. The antenna layout should be kept away from digital signal lines and power lines to reduce interference.
3. Thermal Considerations: At +13 dBm continuous transmission, the QFN package generates heat. The PCB bottom layer should be designed with sufficient grounding vias (Thermal Vias) to assist heat dissipation.
4. Channel Setting: In fixed channel mode, ensure pin levels are set correctly. In SPI mode, a simple register configuration program is required.
5. Regulatory Compliance: Power limits for the 5.8 GHz band vary by country (e.g., Europe CE limits to 10 mW/+10 dBm, US FCC allows 25 mW/+14 dBm). Output power must be configured via pins or registers to ensure compliance with the target market.
6. Procurement: Different batches and package sizes exist (e.g., length from 4.4mm to 8.9mm). Confirm specific dimensions match the PCB layout. Some distributors may misclassify it as a "Memory IC" or "RTC Clock"; always refer to the official RichWave datasheet.