THS770006_14 Datasheet, PDF (18/40 Pages) Texas Instruments – Broadband, Fully-Differential, 14-/16-Bit ADC DRIVER AMPLIFIER

THS770006
SBOS520B – JULY 2010 – REVISED JANUARY 2012
THEORY OF OPERATION
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GENERAL DESCRIPTION
The THS770006 is a fixed-gain of +6dB, wideband, fully-differential amplifier designed and optimized specifically
for driving 14-bit and 16-bit ADCs at input frequencies up to 200MHz. This device provides high bandwidth, low
distortion, and low noise, which are critical parameters in high-speed data acquisition systems that require very
high dynamic range, such as wireless base stations and test and measurement applications. It also makes an
excellent differential amplifier for general-purpose, high-speed differential signal chain and short line-driver
applications. The device has an operating power-supply range of 4.75V to 5.5V. The THS770006 has proprietary
circuitry to provide very fast recovery from overdrive conditions and has a power-down mode for power saving.
The THS770006 is offered in a Pb-free (RoHS compliant) and green, QFN-24 thermally-enhanced package. It is
characterized for operation over the industrial temperature range of –40°C to +85°C.
The amplifier uses two negative-feedback loops. One is for the primary differential amplifier and the other
controls the common-mode operation.
Primary Differential Amplifier
The primary amplifier of the THS770006 is a fully-differential op amp with on-chip gain setting resistors (R_F =
100Ω and R_G = 50Ω) that fix the differential gain at 2V/V, or 6dB, by use of negative feedback.
V_OCM Control Loop
The output common-mode voltage is controlled through a second negative-feedback loop. The output
common-mode voltage is internally sensed and compared to the V_OCM pin. The loop then works to drive the
difference, or error voltage, to zero in order to maintain the output common-mode voltage = V_OCM (within the loop
gain and bandwidth of the loop). For more details on fully-differential amplifier theory and use, see application
report SLOA054, Fully-Differential Amplifiers, available for download from www.ti.com.
OPERATION
Differential to Differential
The THS770006 is a fixed gain of 6dB, fully-differential amplifier that can be used to amplify differential input
signals to differential output signals. A basic block diagram of the circuit is shown in Figure 34. The differential
input to differential output configuration gives the best performance; the signal source and load should be
balanced.
Differential
Input
V_IN-
V_IN+
50W
50W
100W
100W
Differential
Output
V_OUT+
V_OUT-
THS770006
Figure 34. Differential Input to Differential Output Amplifier
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