The **BF908-R** is an N-channel dual-gate MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) primarily designed for high-frequency amplification and mixing applications in the VHF and UHF ranges. ### 1. Key Technical Specifications The "R" suffix typically refers to the pinning configuration (reverse pinning) or specific packaging orientation. Below are the standard electrical characteristics for the BF908 series: | Parameter | Symbol | Maximum Rating | Unit | | :--- | :--- | :--- | :--- | | Drain-Source Voltage | $V_{DS}$ | 12 | V | | Drain Current | $I_D$ | 30 | mA | | Total Power Dissipation | $P_{tot}$ | 200 | mW | | Forward Transfer Admittance | $|y_{fs}|$ | 21 to 30 | mS | | Gate 1 Leakage Current | $I_{G1SS}$ | < 10 | nA | | Noise Figure (at 800 MHz) | $NF$ | 1.5 (typ) | dB | --- ### 2. Functional Features * **Dual-Gate Structure:** The device features two gates. Gate 1 is used for the signal input, while Gate 2 is often used for **Automatic Gain Control (AGC)** or as a local oscillator input in mixing applications. * **Integrated Protection:** Most versions of the BF908 include integrated back-to-back diodes between the gates and the source to protect the thin oxide layer from electrostatic discharge (ESD). * **High Gain / Low Noise:** It is optimized for low-noise performance, making it ideal for the front-end stages of radio receivers. --- ### 3. Pinout Configuration (SOT143 Package) The BF908-R is typically housed in a 4-lead surface-mount package. | Pin Number | Designation | Description | | :--- | :--- | :--- | | 1 | Source | Connected to ground (usually shared with the substrate) | | 2 | Drain | Output terminal | | 3 | Gate 2 | Control gate (AGC or LO input) | | 4 | Gate 1 | Signal input gate | --- ### 4. Typical Applications 1. **VHF/UHF Tuners:** Used in television and radio receivers for signal amplification. 2. **Mixers:** Due to the dual-gate architecture, it can efficiently mix two frequencies (e.g., RF and LO) with high isolation. 3. **Variable Gain Amplifiers:** Gate 2 allows for precise control of the gain without significantly affecting the input impedance at Gate 1.