NS LMH6553 900MHz差分放大方案

NS公司的LMH6553是900MHz带输出可调钳位的全差分放大器.LMH6553具有极好的带宽,失真和噪音性能,能驱动多达14位的ADC,广泛用在汽车电子,通信,医疗,测试测量,视频以及LIDAR等.本文介绍了LMH6553的主要特性, 单端输入差分输入驱动ADC的电路图, 单端输入差分输出电路图以及高速差分放大器评估板LMH6553SDEVAL的电路图以及PCB布线的设计考虑.

LMH6553:900 MHz Fully Differential Amplifier With Output Limiting Clamp The LMH6553 is a 900 MHz differential amplifier with an integrated adjustable output limiting clamp. The clamp increases system performance and provides transient over-voltage protection to following stages. The internal clamp feature of the LMH6553 reduces or eliminates the need for external discrete overload protection networks. When used to drive ADCs, the amplifiers output clamp allows low voltage ADC inputs to be protected from being overdriven and damaged by large input signals appearing at the system input. Fast overdrive recovery of 600 ps ensures the amplifier output rapidly recovers from a clamping event and quickly resumes to follow the input signal. The LMH6553 delivers exceptional bandwidth, distortion, and noise performance ideal for driving ADCs up to 14-bits. The LMH6553 could also be used for automotive, communication, medical, test and measurement, video, and LIDAR applications.
With external gain set resistors and integrated common mode feedback, the LMH6553 can be configured as either a differential input to differential output or single ended input to differential output gain block. The LMH6553 can be AC or DC coupled at the input which makes it suitable for a wide range of applications including communication systems and high speed oscilloscope front ends. The LMH6553 is available in 8-pin PSOP and 8-pin LLP packages, and is part of our LMH  high speed amplifier family.

LMH6553主要特性:
■900 MHz −3 dB small signal bandwidth @ AV = 1
■670 MHz −3 dB large signal bandwidth @ AV = 1
■−79 dB THD 20 MHz
■−92 dB IMD3 fc = 20 MHz
■10 ns settling time to 0.1%
■600 ps clamp overdrive recovery time
■40 mV clamp accuracy with 100% Overdrive
■−0.1 mV/°C clamp temperature drift
■4.5 to 12 supply voltage operation
LMH6553应用:
■Differential ADC driver
■Video over twisted pair
■Differential line driver
■Single end to differential converter
■High speed differential signaling
■IF/RF amplifier
■SAW filter buffer/driver
■CCD Output Limiting Amplifier



图2.LMH6553单端输入差分输出电路图

高速差分放大器评估板LMH6553SDEVAL
LMH6553SDEVAL High Speed Differential Amplifier Evaluation Board
The LMH6553SDEVAL evaluation board is designed to aid in the characterization of National Semiconductor’s LMH6553 fully differential amplifier with output limiting clamp in an 8-pin LLP package. The LMH6553 is part of the LMH  high speed amplifier family.
Use the evaluation board as a guide for high frequency layout and as a tool to aid in device testing and characterization. The evaluation board schematic is shown below in Figure 3. Refer to the product datasheets for recommended for component values.
Layout Considerations
Printed circuit board layout and supply bypassing play major roles in determining high frequency performance. When designing your own board use these evaluation boards as a guide and follow these steps to optimize high frequency performance:
1. Symmetry is of the utmost importance.
2. Use precision resistors 0.1% or 0.01%.
3. Use a ground plane.
4. Include large ( ~ 10 μF) capacitors on both supplies (C1 and C3).
5. Near the device use 0.01 μF ceramic capacitors from both supplies to ground (C2, C4).
6. A capacitor between V+ and V− (C5) is optional, but will help lower distortion.
7. Remove the ground and power planes from under and around the part, especially the input and output pins.
8. Minimize all trace lengths.
9. Use terminated transmission lines for long traces.