LMH2832 Datasheet, PDF (29/46 Pages) Texas Instruments – LMH2832 Fully Differential, Dual, 1.1-GHz, Digital Variable-Gain Amplifier

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10 Application and Implementation
LMH2832
SBOS709A – JULY 2016 – REVISED JULY 2016
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
The LMH2832 is designed as a general-purpose, analog-to-digital converter (ADC) driver that also meets the
performance requirements for DOCSIS 3.X upstream CMTS solutions. This section describes various
requirements and considerations for using the LMH2832 and also some design examples.
10.1.1 Driving ADCs
When the amplifier is driving an ADC, the key points to consider for implementation are the signal-to-noise ratio
(SNR), spurious-free dynamic range (SFDR), and ADC input considerations, as described in this section.
A typical application of the LMH2832 involves driving a wideband, 14-bit ADC (such as the ADS54J40), as
shown in Figure 59. The LMH2832 can drive the full Nyquist bandwidth of ADCs with sampling rates up to
900 MSPS. If the front-end bandwidth of the ADC is more than 450 MHz, then use a simple noise filter to
improve SNR. Otherwise, the ADC can be connected directly to the amplifier output pins with appropriate
matching resistors to limit the full-scale input of the ADC. Note that the LMH2832 inputs must be driven
differentially using a balun or fully differential amplifiers (FDAs). For dc-coupled applications, an FDA (such as
the LMH3401 or LMH5401) that can convert a single-ended input to a differential output with low distortion is
preferred.
VS+ = 5V
ZS = 50-Ÿ _1:3
INPx
10
OUTPx ^RO
½ LMH2832
+
- ^OUT_AMP
LPF
INMx
10
OUTMx _RO
ADC
SPI
GND
Copyright © 2016, Texas Instruments Incorporated
Figure 59. ADC Driver with a 50-Ω Source
Copyright © 2016, Texas Instruments Incorporated
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