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.
MAX2034
Quad-Channel, Ultra-Low-Noise Amplifier with
Digitally Programmable Input Impedance
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