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

Functional Diagram

Digitally Programmable Input Impedance

The MAX2034 features an on-chip digitally programma-

ble input impedance, which makes the part compatible

D2/D1/D0

with a variety of source impedances ranging from 50Ω

PD

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

ZF1

impedance can be supported by using an off-chip

external feedback resistor, RF. To utilize this feature, set

D2, D1, and D0 to any of the four external resistor-con-

IN1

OUT1-

trolled states shown in Table 1. The value of the off-chip

INC1

feedback resistor can be determined by using the fol-

lowing relationship:

OUT1+

RF = (1 + (A / 2)) x RS

MAX2034

INB1

where RS is the source impedance, and A is the gain of

the amplifier (A = 9) defined with a differential output.

Noise Figure

The MAX2034 is designed to provide maximum input

ZF2

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

IN2

OUT2-

been optimized for source impedances from 50Ω to

INC2

1000Ω. Additionally, the noise contribution of the

OUT2+

matching resistor is effectively divided by 1 + (A / 2).

Using this scheme, typical noise figure of the amplifier

INB2

is approximately 2.2dB for RIN = RS = 200Ω. Table 2

illustrates the noise figure for other input impedances.

Table 2. Noise Figure vs. Source and

ZF3

Input Impedances

Rs (Ω)

RIN (Ω)

NF (dB)

IN3

OUT3-

50

50

4.1

INC3

100

100

2.9

OUT3+

200

200

2.2

1000

1000

1.4

INB3

Input Clamp

The MAX2034 includes configurable integrated input-

clamping diodes. The diodes are clamped to ground at

ZF4

±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

IN4

OUT4-

place charge on the input-coupling capacitor, causing

INC4

longer transmit overload recovery times. Input signals

OUT4+

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-

INB4

ferred, simply leave INC1–INC4 unconnected.

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