LMH6518 - 900 MHz, Digitally Controlled, Variable Gain Amplifier

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.

• 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