Video-line-driving-amplifier

Q1 and Q2 create a differential stage that transitions into the LT1010. The capacitively terminated feedback divider provides a gain of 1, while permitting AC gains of up to 10. With a 20-ohm bias resistor, the circuit outputs 1 V peak-to-peak into a standard 75-ohm video load. For applications that are sensitive to NTSC specifications, reducing the bias resistor value can enhance performance. At a gain of approximately 2, the gain remains within 0.5 dB up to 10 MHz, with the -3 dB point occurring at 16 MHz. At a gain of approximately 10, the gain is stable within ±0.5 dB up to 4 MHz, and the -3 dB point is at 8 MHz. The peaking adjustment should be optimized under loaded output conditions.

The circuit described consists of a differential amplifier stage formed by transistors Q1 and Q2, which serve to amplify the input signal while minimizing noise and distortion. The LT1010 operational amplifier is utilized for its high-speed performance and low offset voltage, making it suitable for video applications. The feedback divider is capacitively terminated, which is a common technique used to stabilize gain and bandwidth while allowing for a controlled feedback path.

The gain settings of the circuit are designed to accommodate different operational requirements. With a gain of approximately 1, the circuit operates in a unity gain configuration, which is often used for buffering applications. This configuration is beneficial for maintaining signal integrity when interfacing with other stages of a circuit. When the gain is increased to approximately 10, the circuit can provide significant amplification for video signals, making it suitable for driving loads such as video displays or transmission lines.

The choice of a 20-ohm bias resistor is critical in setting the quiescent operating point of the transistors, ensuring they operate within their optimal range. The specification of delivering 1 V peak-to-peak into a 75-ohm load is essential for compatibility with standard video equipment, which typically operates at this impedance. Adjusting the bias resistor value allows for fine-tuning of the circuit's performance, particularly in applications where adherence to NTSC standards is crucial.

Frequency response characteristics are vital for maintaining signal quality in video applications. The specified performance at gains of 2 and 10 indicates the circuit's ability to maintain a relatively flat gain across specified frequency ranges, which is important for avoiding signal degradation. The -3 dB points at 16 MHz and 8 MHz for gains of 2 and 10, respectively, define the bandwidth limitations of the circuit, indicating where the gain begins to roll off.

The optimization of peaking adjustment under loaded conditions is an important consideration, as it allows for the compensation of any potential overshoot or ringing that may occur in high-frequency applications. Properly tuning this adjustment ensures that the output signal remains stable and free from distortion, which is critical in high-fidelity video applications. This comprehensive approach to circuit design ensures robust performance across various operating conditions, making the described circuit well-suited for its intended applications.Q1 and Q2 form a differential stage which single- ends into the LT1010. The capacitively terminated feedback divider gives the circuit a de gain of 1, while allowing ac gains up to 10. Using a 20-fl bias resistor, the circuit delivers 1 V pk-pk into a typical 75-fl video load. For applications sensitive to NTSC requirements, dropping the bias resistor value will aid performance.

At A ~ 2, the gain is within 0.5 dB to 10 MHz and the -3 dB point occurs at 16 MHz. At A ~ 10, the gain is flat, within ±0.5 dB to 4 MHz, and the -3 dB point occurs at 8 MHz. The peaking adjustment should be optimized under loaded output conditions. 🔗 External reference