MAX2034CTM-T 查看數據表（PDF） - Maxim Integrated

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MAX2034CTM-T

Quad-Channel, Ultra-Low-Noise Amplifier with Digitally Programmable Input Impedance

Maxim Integrated 

Quad-Channel, Ultra-Low-Noise Amplifier with

Digitally Programmable Input Impedance

Integrated Input Damping Capacitor

At high frequencies, gain peaking can occur due to an

active input termination becoming less effective when

the gain rolls off. Although an external shunting capaci-

tor can be used to mitigate this effect, different input

impedance modes require different capacitor values.

The MAX2034 integrates a damping capacitor for each

of the four programmed input impedance modes. When

the input impedance is programmed by applying the

appropriate D2/D1/D0, an optimal capacitor value is

also chosen for the particular input impedance mode,

eliminating the need for external capacitors.

Overload Recovery

The device is also optimized for quick overload recov-

ery for operation under the large input signal conditions

that are typically found in ultrasound input-buffer imag-

ing applications. Internal signal clipping is symmetrical.

Input overloads can be prevented with the input-clamp-

ing diodes. See the Typical Operating Characteristics

that illustrate the rapid recovery time from a transmit-

related overload.

Sleep Mode

The sleep mode function allows the MAX2034 to be

configured in a low-power state when the amplifiers are

not being used. In sleep mode, all amplifiers are pow-

ered down, the total supply current of the device

reduces to 0.8mA, and the input impedance of each

amplifier is set at high impedance. Drive the PD input

high to activate sleep mode. For normal operation,

drive the PD input low.

Applications Information

Analog Input Coupling

AC-couple to ground the analog bypass input by con-

necting a 0.1µF capacitor at the INB1–INB4 input to

GND (0.1µF recommended). Since the amplifiers are

designed with a differential input stage, bypassing the

INB1–INB4 inputs configures the MAX2034 for single-

ended inputs at IN1–IN4.

Connect the IN1–IN4 inputs to their source circuits

through 0.1µF series capacitors. Connect the feedback

ports ZF1–ZF4 to the source circuits through 0.018µF

capacitors. (These capacitors will be 1/(5.5) as large as

the input-coupling capacitors. This equalizes the high-

pass filter characteristic of both the input and feedback

input ports, due to the feedback resistance related by a

factor of 1/(5.5) to the input impedance.)

Note that the active input circuitry of the MAX2034 is

stable, and does not require external ferrite beads or

shunt capacitors to achieve high-frequency stability.

The Typical Application Circuit illustrates these cou-

pling capacitors. If a ground-referenced current-limiting

stage precedes the MAX2034 inputs, its output can be

connected to the integrated clamping diodes on pins

INC1–INC4 to facilitate very rapid recovery from tran-

sient overloads associated with transmitter operation in

ultrasound applications.

Analog Output Coupling

The differential outputs of the MAX2034 are capable of

driving a differential load impedance of 200Ω or

greater. The differential output has a common-mode

bias of approximately 2.45V. AC-couple these differen-

tial outputs if the next stage has a different common-

mode input range.

Board Layout

The pin configuration of the MAX2034 is optimized to

facilitate a very compact physical layout of the device

and its associated discrete components. A typical

application for this device might incorporate several

devices in close proximity to handle multiple channels

of signal processing.

The exposed paddle (EP) of the MAX2034’s thin QFN-

EP package provides a low thermal-resistance path to

the die. It is important that the PC board on which the

MAX2034 is mounted be designed to conduct heat

from the EP. In addition, provide the EP with a low-

inductance path to electrical ground. The EP MUST be

soldered to a ground plane on the PC board, either

directly or through an array of plated via holes.

ULTRASOUND IMD3

-25dB

F1 - (F2 - F1)

F1

F2

F2 + (F2 - F1)

Figure 1. Ultrasound IMD3 Measurement Technique

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