THS7530-Q1 Datasheet, PDF (11/30 Pages) Texas Instruments – THS7530-Q1 High-Speed, Fully Differential, Continuously Variable Gain Amplifier

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8 Detailed Description
THS7530-Q1
SLOS932 – DECEMBER 2015
8.1 Overview
The THS7530-Q1 device is a fully-differential amplifier with 300-MHz bandwidth and with continually-variable
gain from 11.6 dB to 46.5 dB. This amplifier together with an automatic gain control (AGC) circuit will precisely
established a desired amplitude at its output.
The input architecture is a modified Gilbert cell. The output from the Gilbert cell is converted to a voltage and
buffered to the output as a fully-differential signal. A summing node between the outputs is used to compare the
output common-mode voltage to the V_OCM input. The V_OCM error amplifier then servos the output common-mode
voltage to maintain it equal to the V_OCM input. Left unterminated, V_OCM is set to midsupply by internal resistors.
The gain control input is conditioned to give linear-in-dB gain control (block H). The gain control input is a
differential signal from 0 V to 0.9 V which varies the gain from 11.6 dB to 46.5 dB.
V_CL+ and V_CL– provide inputs that limit the output voltage swing of the amplifier.
8.2 Functional Block Diagram
V_CL+
V_CL-
V_S+
x1
Output
Buffer
V_OUT+
V_IN+
V_IN-
PD
V_S-
V_G+
V_G-
Power
Control
H
V_OCM Error
Amplifier
V_OUT-
V_OCM
THS7530
8.3 Feature Description
The main features of the THS7530-Q1 device are continually-variable gain control, common-mode voltage
control, output voltage clamps, and power-down mode.
8.3.1 Continually-Variable Gain Control
The amplifier gain in dB is a linear function of the gain control voltage, which has a range of 0 V to 0.9 V. The
slope of the gain control input is 38.8 dB/V with a gain range of 11.6 dB to 46.5 dB, which is 3.8 to 211.3 V/V,
respectively. The bandwidth of the gain control is 15 MHz, typically.
The gain control is a differential input to reduce noise due to ground bounce, coupling, and so forth. The negative
gain-control input V_G– can be below the negative supply by as much as 600 mV.
8.3.2 Common-Mode Voltage Control
The common-mode voltage control sets the common-mode voltage of the differential output. The gain of the
control voltage is 1 V/V with a range of 1.75 V to 3.25 V above the negative supply. If unconnected, the common-
mode voltage control is at mid-supply, typically 2.5 V above the negative supply. The bandwidth of the common-
mode voltage control is an impressive 32 MHz.
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