LMH6518_15 Datasheet, PDF (1/41 Pages) Texas Instruments – LMH6518 900 MHz, Digitally Controlled, Variable Gain Amplifier

LMH6518
www.ti.com
SNOSB21C – MAY 2008 – REVISED JULY 2013
LMH6518 900 MHz, Digitally Controlled, Variable Gain Amplifier
Check for Samples: LMH6518
FEATURES
1
•2 Gain Range 40 dB
• Gain Step Size 2 dB
• Combined Gain Resolution with
Gsample/Second ADC’s 8.5 mdB
• Min Gain −1.16 dB
• Max Gain 38.8 dB
• −3 dB BW 900 MHz
• Rise/Fall Time <500 ps
• Recovery Time <5 ns
• Propagation Delay Variation 100 ps
• HD2 @ 100 MHz −50 dBc
• HD3 @ 100 MHz −53 dBc
• Input-Referred Noise (Max Gain) 0.98 nV/√Hz
• Over-Voltage Clamps for Fast Recovery
• Power Consumption — Auxiliary Turned Off
1.1W0.75W
APPLICATIONS
• Oscilloscope Programmable Gain Amplifier
• Differential ADC Drivers
• High Frequency Single-Ended Input to
Differential Conversion
• Precision Gain Control Applications
• Medical Applications
• RF/IF Applications
DESCRIPTION
The LMH6518 is a digitally controlled variable gain
amplifier whose total gain can be 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 a Texas Instruments
Gsample/second (Gsps) ADC with adjustable full
scale (FS) range, the LMH6518 gain adjustment will
accommodate 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 via a SPI-1
compatible serial bus. A signal path combined gain
resolution of 8.5 mdB can be achieved when the
LMH6518’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.
Functional Block Diagram
GND
VDD
5,8
12
LMH6518
Hi Gain
or
Low Gain
6
+IN
7
-IN
Input
Preamp
Overvoltage
Clamp
10 Step
2 dB/Step
VCC
3,4
Common Mode
Control
Bandwidth
Limiting
Circuitry
VCM_Aux
16
13 _VCM
Overvoltage
Clamp
Output Amp
50:
15 _+OUT
MAIN OUT
50:
14 _-OUT 72µ$'&¶
Serial Peripheral
Interface
Aux Amp
Overvoltage
Clamp
50:
50:
1
+OUT Aux
AUXILIARY
2 _{-OUT Aux} OUTPUT
10 9
11
SDIO CS SCLK
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2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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