1 Features

• Gain Range: 40 dB
• Gain Step Size: 2 dB
• Combined Gain Resolution With Gsps ADCs:
  8.5 mdB
• Minimum Gain: −1.16 dB
• Maximum Gain: 38.8 dB
• −3 dB BW: 900 MHz
• Rise and Fall Time: <500 ps
• Recovery Time: <5 ns
• Propagation Delay Variation: 100 ps
• HD2 at 100 MHz: −50 dBc
• HD3 at 100 MHz: −53 dBc
• Input-Referred Noise (Maximum Gain):
  0.98 nV/√Hz
• Overvoltage Clamps for Fast Recovery
• Power Consumption: Auxiliary Turned Off
  1.1 W to 0.75 W

2 Applications

• Oscilloscope Programmable Gain Amplifiers
• Differential ADC Drivers
• High-Frequency Single-Ended Input to Differential Conversion
• Precision Gain Control Applications
• Medical Applications
• RF/IF Applications

3 Description

The LMH6518 device is a digitally controlled variable gain amplifier whose total gain is varied from
−1.16 dB to 38.8 dB for a 40 dB range in 2-dB steps. The −3-dB bandwidth is 900 MHz at all gains. Gain accuracy at each setting is typically 0.1 dB. When used in conjunction with TI's Gsample/second (Gsps) ADC with adjustable full-scale (FS) range, the LMH6518 gain adjustment accommodates full scale input signals from 6.8 mV_PP to 920 mV_PP to get
700 mV_PP nominal at the ADC input. The auxiliary output (+OUT AUX and −OUT AUX) follows the main output and is intended for use in oscilloscope trigger function circuitry but may have other uses in other applications.

The LMH6518 gain is programmed through a SPI-1 compatible serial bus. A signal path combined gain resolution of 8.5 mdB is achieved when the device's gain and the Gsps ADC’s FS input are both manipulated. Inputs and outputs are DC-coupled. The outputs are differential with individual common mode (CM) voltage control (for main and auxiliary outputs), and have a selectable bandwidth limiting circuitry (common to both main and auxiliary) of 20, 100, 200, 350, 650, 750 MHz or full bandwidth.

1. For all available packages, see the orderable addendum at the end of the data sheet.

Functional Block Diagram