Ultra-High-Speed, Low-Distortion – Differential-to-Single-Ended Line Receivers with Enable

The project presented here is a differential line receiver that offers unparalleled high-speed, low-distortion performance and is ideally suited for digital, video, and RF signal-processing applications. These receivers offer a small-signal bandwidth of 550MHz and have a high slew rate of up to 2000-3800V/µs. The board’s 120mA output capability allows it to be directly coupled to data acquisition systems. The project has been designed using the MAX4445 chip, which has a three-op amp instrumentation amplifier architecture. These ICs have symmetrical differential inputs and a single-ended output. The project operates from ±5V supply and is capable of driving a 100Ω load to ±3.7V.  MAX4445 is compensated for gains of +2V/V or greater, set by an external resistor R3. A low-power enable mode reduces current consumption to 3.5mA. Using current-feedback techniques, the MAX4445 achieves a 550MHz bandwidth while maintaining up to a 5000V/µs slew rate. Excellent differential gain/phase and noise specifications make these amplifiers ideal for a wide variety of digital, video, and RF signal-processing applications. It is important to make a Gold-plated high-quality PCB and use high-grade components and connectors to operate at high frequency.

Low-Power Enable Mode

The chip is disabled when Enable pin goes low. This reduces the supply current to only 3.5mA. In this case, the output becomes high impedance.  The effective output impedance for the MAX4445 is 1.8kΩ plus R_GAIN (Resistor R3)

Setting Gain (Resistor R3) – Default Gain +2V/V

The MAX4445 is stable with a minimum gain configuration of +2V/V. R_GAIN R3, connected between the RG pins. Gain can be changed using the below formula:

Gain = (1 + 600 / R_GAIN)

Coaxial Line Driver

The project is well suited to drive coaxial cables. The high output current capability can easily drive the 75Ω characteristic impedance of common coaxial cables. Adjust the gain of the MAX4445 to compensate for cable losses to maintain the required levels at the input of the next stage.

Key Features

• Operating Power Supply +/-5V DC (Dual 5V DC)
• Output Current Drive 90 to 120mA (Load 30 Ohms)
• Output Swing +/-3.3V
• 2000-3800V/µs Slew Rate
• External Gain Selection AVCL ≥ +2V/V
• 550MHz -3dB Bandwidth
• -60dB SFDR at 5MHz
• Low Differential Gain/Phase: 0.07%/0.05°
• Low Noise: 25nV/ at fIN = 100kHz
• Low-Power Disable Mode Reduces Quiescent Current to 3.5mA
• PCB Dimensions 36.20 X 28.89 mm

Applications

• Data Acquisition
• Differential to Single-Ended Conversion
• High-Speed Differential Line Receiver
• High-Speed Instrumentation Amplifier
• Medical Instrumentation
• Twisted-Pair to Coaxial Converter

Schematic

Parts List

Connections

Gerber View

Photos

Video

MAX4445 Datasheet

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