THS4031_16 Datasheet, PDF (28/47 Pages) Texas Instruments – THS403x 100-MHz Low-Noise High-Speed Amplifiers

THS4031, THS4032
SLOS224H – JULY 1999 – REVISED JUNE 2016
www.ti.com
11 Power Supply Recommendations
The THS4031 can operate off a single supply or with dual supplies as long as the input CM voltage range
(CMIR) has the required headroom to either supply rail. Operating from a single supply can have numerous
advantages. With the negative supply at ground, the DC errors due to the –PSRR term can be minimized.
Supplies should be decoupled with low inductance, often ceramic, capacitors to ground less than 0.5 inches from
the device pins. TI recommends using a ground plane. In most high speed devices, it is advisable to remove the
ground plane close to device sensitive pins such as the inputs. An optional supply decoupling capacitor across
the two power supplies (for split supply operation) improves second harmonic distortion performance.
12 Layout
12.1 Layout Guidelines
In order to achieve the levels of high-frequency performance of the THS403x, it is essential that proper printed-
circuit board (PCB) high-frequency design techniques be followed. A general set of guidelines is given below. In
addition, a THS403x evaluation board is available to use as a guide for layout or for evaluating the device
performance.
• Ground planes: TI highly recommends using a ground plane on the board to provide all components with a
low inductive ground connection. However, in the areas of the amplifier inputs and output, the ground plane
can be removed to minimize the stray capacitance.
• Proper power-supply decoupling: Use a 6.8-μF tantalum capacitor in parallel with a 0.1-μF ceramic capacitor
on each supply terminal. It may be possible to share the tantalum among several amplifiers depending on the
application, but a 0.1-μF ceramic capacitor should always be used on the supply terminal of every amplifier.
In addition, the 0.1-μF capacitor should be placed as close as possible to the supply terminal. As this distance
increases, the inductance in the connecting trace makes the capacitor less effective. The designer should
strive for distances of less than 0.1 inch between the device power terminals and the ceramic capacitors.
• Sockets: TI does not recommend sockets for high-speed operational amplifiers. The additional lead
inductance in the socket pins will often lead to stability problems. Surface-mount packages soldered directly
to the printed-circuit board is the best implementation.
• Short trace runs/compact part placements: Optimum high-frequency performance is achieved when stray
series inductance has been minimized. To realize this, the circuit layout should be made as compact as
possible, thereby minimizing the length of all trace runs. Particular attention should be paid to the inverting
input of the amplifier. Its length should be kept as short as possible. This will help to minimize stray
capacitance at the input of the amplifier.
• Surface-mount passive components: TI recommends using surface-mount passive components for high-
frequency amplifier circuits for several reasons. First, because of the extremely low lead inductance of
surface-mount components, the problem with stray series inductance is greatly reduced. Second, the small
size of surface-mount components naturally leads to a more compact layout thereby minimizing both stray
inductance and capacitance. If leaded components are used, TI recommends that the lead lengths be kept as
short as possible.
12.2 Layout Example
An evaluation board is available for the THS4031 and THS4032. This board has been configured for very low
parasitic capacitance in order to realize the full performance of the amplifier. A schematic of the evaluation board
is shown in Figure 65. The circuitry has been designed so that the amplifier may be used in either an inverting or
noninverting configuration. For more information, refer to the THS4031 EVM User's Guide or the THS4032 EVM
User's Guide. To order the evaluation board, contact your local TI sales office or distributor.
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