Detailed Description

The MAX3654 is a broadband, high-linearity, low-noise

transimpedance amplifier. The transimpedance (gain)

can be adjusted between 43.5dB

Ω and 62dBΩ using

the voltage at an external control input (VAGC). When

connected as shown in the Typical Application Circuit,

optical input levels from -6dBm to +2dBm will produce

a minimum output of 14dBmV/channel, and 4dB tilt

compensation. Gain deviation over frequency from

47MHz to 870MHz is less than ±0.75dB.

Low-Noise Variable Gain Amplifier

The input stage is a low-noise analog transimpedance

amplifier (TIA) connected differentially to the analog

photodiode. Desired performance can be achieved

VAGC and Hysteresis Control

The gain-control pin VAGC sets overall TIA gain imple-

mented as three switchable gain stages, each with a

continuously variable gain control, as shown in Figure 3.

This produces a continuously variable gain ranging

from 62dB

Ω (at VAGC = 0.175V) to 43.5dBΩ at

(VAGC=1.4V). A set of comparators examines the

VAGC input to select a gain stage. As the voltage at

VAGC crosses the two locations in the gain vs. VAGC

curve, where the gain stage changes (350mV and

700mV), there will be small deviations in the output

which may lead to a brief interruption of CATV signals.

See the Typical Operating Characteristics for Gain vs.

Control Voltage.

A hysteresis control input is provided to limit dithering

when the optical level is close to a gain-switching point.

Hysteresis is minimum (0.13dB) when this pin is open.

RF Output and Cable Tilt Compensation

With a typical photodiode, the gain at 870MHz is 4dB

higher than at 47MHz. The overall frequency response

of the TIA is within ±0.75dB of a straight line connecting

the values at 47MHz and 870MHz.

Mute

In normal operation, the TTL MUTE pin is held high.

When MUTE is low, the output signal is attenuated by

more than 45dB.

47MHz to 870MHz Analog CATV

Transimpedance Amplifier

6

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Pin Description

PIN

NAME

FUNCTION

1, 4, 9, 12

+5.0V Power Supply

2

IN+

Positive Analog Photodiode Input Connection. Typically connected to photodiode cathode.

3

IN-

Negative Analog Photodiode Input Connection. Typically connected to photodiode anode.

5

VAGC

AGC Control Input. Range is 0 to 1.4V. See the Typical Operating Characteristics Gain vs. Control

Voltage graph.

6

MUTE

Mute Control Input, TTL. MUTE < 0.8V to mute output.

7

HYST

AGC Hysteresis Control Input. A resistor from HYST to GND controls the hysteresis level.

8, 14, 16

GND

Ground

10

OUT-

Negative RF Output. The voltage on this pin decreases with increasing optical power when IN+ is

connected to the photodiode cathode.

11

OUT+

Positive RF Output. The voltage on this pin increases with increasing optical power when IN- is

connected to the photodiode anode.

13

TEST1

Reserved for Test. Connect to GND for normal operation.

15

TEST2

Reserved for Test. Connect to GND for normal operation.

EP

EP

Exposed Pad. The exposed pad must be soldered to the circuit-board ground for proper thermal and

electrical performance.