## Overview of the ADG904-R The **ADG904-R** is a high-performance, wideband CMOS analog switch designed as a **4:1 Multiplexer**. It is specifically engineered to handle high-frequency signals, making it suitable for RF (Radio Frequency) and microwave applications. The "-R" suffix usually denotes specific packaging or compliance standards (such as RoHS compliance or Tape and Reel packaging), but the core functionality remains consistent with the ADG904 series. --- ### 1. Key Technical Specifications Below are the primary electrical characteristics of the ADG904-R: | Feature | Specification | | :--- | :--- | | **Configuration** | 4:1 Multiplexer (SP4T) | | **Bandwidth (-3 dB)** | Up to 2.5 GHz | | **Insertion Loss** | ~0.8 dB @ 1 GHz | | **Isolation** | 37 dB @ 1 GHz | | **Supply Voltage** | 1.65 V to 2.75 V | | **Package Options** | 20-lead LFCSP or TSSOP | | **Control Logic** | CMOS/LVTTL Compatible | --- ### 2. Functional Components and Architecture The internal architecture of the ADG904-R is optimized for signal integrity at high frequencies. #### A. Absorptive vs. Reflective Switches The ADG904-R is an **absorptive switch**. - It contains **50 Ω terminated shunt legs**. - When a channel is "OFF," the port is terminated to 50 Ω rather than being left open. This prevents signal reflections that could degrade the performance of the rest of the RF chain. #### B. Control Interface It uses a simple parallel control interface: - **A0 and A1 Pins:** Binary address pins used to select one of the four channels. - **EN Pin (Enable):** When pulled low, all channels are disconnected, and all ports are terminated to 50 Ω. #### C. CMOS Construction Unlike GaAs (Gallium Arsenide) switches, the ADG904 is built on a standard CMOS process. This allows for: - Very low power consumption (< 1 µA). - Integration with standard digital logic without the need for negative bias voltages. --- ### 3. Application Areas The ADG904-R is commonly integrated into circuits requiring high-speed signal routing: 1. **Wireless Communications:** Switching between different antennas or filters in mobile devices. 2. **Test Equipment:** Routing high-speed clock signals or RF test signals in automated test equipment (ATE). 3. **Base Stations:** Signal path selection in cellular infrastructure. 4. **High-Speed Data:** Routing differential or single-ended high-speed digital signals. --- ### 4. Design Considerations When implementing the ADG904-R in a PCB layout, consider the following: * **Impedance Matching:** Ensure all PCB traces leading to the pins are designed for 50 Ω characteristic impedance. * **Decoupling:** Place a 0.1 µF capacitor as close as possible to the $V_{DD}$ pin to minimize noise. * **Grounding:** The LFCSP package usually has an exposed paddle. This must be soldered to the PCB ground plane to ensure both electrical grounding and thermal dissipation.