max2034ctmt Maxim Integrated Products, Inc., max2034ctmt Datasheet - Page 8

• Manufacturer Part Number: max2034ctmt
• Description: Quad-channel, Ultra-low-noise Amplifier With Digitally Programmable Input Impedance
• Manufacturer: Maxim Integrated Products, Inc.

Quad-Channel, Ultra-Low-Noise Amplifier with
Digitally Programmable Input Impedance
8
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INC1
INB1
INC2
INB2
INC3
INB3
INC4
INB4
ZF1
ZF2
ZF3
ZF4
IN1
IN2
IN3
IN4
PD
Functional Diagram
MAX2034
D2/D1/D0
OUT1-
OUT1+
OUT2-
OUT2+
OUT3-
OUT3+
OUT4-
OUT4+
The MAX2034 features an on-chip digitally programma-
ble input impedance, which makes the part compatible
with a variety of source impedances ranging from 50Ω
to 1kΩ. The input impedance can be programmed for
50Ω, 100Ω, 200Ω, or 1kΩ through the digital inputs D2,
D1, and D0. See Table 1 for programming details. In
addition to these fixed values, virtually any other input
impedance can be supported by using an off-chip
external feedback resistor, R
D2, D1, and D0 to any of the four external resistor-con-
trolled states shown in Table 1. The value of the off-chip
feedback resistor can be determined by using the fol-
lowing relationship:
where R
the amplifier (A = 9) defined with a differential output.
The MAX2034 is designed to provide maximum input
sensitivity with its exceptionally low noise figure. The
input active devices are selected for very low equiva-
lent input noise voltage and current, and they have
been optimized for source impedances from 50Ω to
1000Ω. Additionally, the noise contribution of the
matching resistor is effectively divided by 1 + (A / 2).
Using this scheme, typical noise figure of the amplifier
is approximately 2.2dB for R
illustrates the noise figure for other input impedances.
The MAX2034 includes configurable integrated input-
clamping diodes. The diodes are clamped to ground at
±275mV. The input-clamping diodes can be used to
prevent large transmit signals from overdriving the inputs
of the amplifiers. Overdriving the inputs could possibly
place charge on the input-coupling capacitor, causing
longer transmit overload recovery times. Input signals
are AC-coupled to the single-ended inputs IN1–IN4, but
are clamped with the INC1–INC4 inputs. See the Typical
Application Circuit. If external clamping devices are pre-
ferred, simply leave INC1–INC4 unconnected.
Table 2. Noise Figure vs. Source and
Input Impedances
Digitally Programmable Input Impedance
Rs (Ω)
1000
100
200
50
S
is the source impedance, and A is the gain of
R
F
= (1 + (A / 2)) x R
R
1000
IN
100
200
50
(Ω)
F
IN
. To utilize this feature, set
= R
S
S
= 200Ω. Table 2
Noise Figure
Input Clamp
NF (dB)
4.1
2.9
2.2
1.4