The **LM591** (often categorized with its close relative, the LM592) is a classic **Video Sense Amplifier** or high-frequency differential amplifier. It is primarily designed for applications requiring high gain and wide bandwidth, such as magnetic head preamplifiers, video circuitry, and high-speed data communications. --- ### 1. Key Technical Specifications The LM591 is known for its high-speed performance and differential input/output configuration. | Parameter | Typical Value | | :--- | :--- | | **Bandwidth** | Up to 120 MHz | | **Voltage Gain** | 100 to 400 (Adjustable) | | **Input Resistance** | 30 kΩ | | **Output Resistance** | 20 Ω | | **Supply Voltage** | ±3V to ±8V | | **Rise Time** | 4.0 ns (approx.) | --- ### 2. Internal Architecture & Pins The device is built using a two-stage common-emitter differential amplifier design. It features internal emitter-follower outputs to provide low output impedance. #### Major Pin Functions: * **Inputs (In+ / In-):** Differential inputs for the signal. * **Outputs (Out+ / Out-):** Differential outputs. * **Gain Select (G1A, G1B, G2A, G2B):** These pins allow the user to select fixed gain levels (e.g., 400 or 100) by shorting specific pins, or to adjust gain precisely using an external resistor. * **V+ / V-:** Power supply pins. --- ### 3. Core Features * **Adjustable Gain:** You can choose between fixed gain settings or use an external resistor between the gain-adjustment pins to set a custom gain. * **No Frequency Compensation Required:** The internal design is stable across its operating range without the need for external capacitors. * **High Common-Mode Rejection:** Effectively filters out noise that is common to both input lines, which is critical in video and data signals. --- ### 4. Typical Applications The LM591 is most commonly found in "legacy" or specialized high-speed analog hardware: 1. **Magnetic Disk Drive Read-Heads:** Amplifying the weak signals pulled from spinning magnetic platters. 2. **Video Amplification:** Used in older CRT monitors and video distribution amplifiers to maintain signal integrity over high frequencies. 3. **Fiber Optic Receivers:** Converting high-speed light pulses (via a photodiode) into usable electrical signals. 4. **Pulse Amplifiers:** Used in laboratory equipment to amplify very short-duration pulses. --- ### 5. Application Circuit Example (Simplified) To set a specific gain, an external resistor $R_G$ is placed between the Gain Select pins: ```text V+ | [ LM591 ] In+ --| |-- Out+ In- --| |-- Out- | Gain| +-|R_G|-+ | | V- ```