MAX3510 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX3510

Upstream CATV Amplifier

Maxim Integrated 

Upstream CATV Amplifier

Table 3. Chip-State Control Bits

SHDN TXEN

D7

D6

D5

D4

D3

D2

D1

D0

GAIN STATE

(DECIMAL)

STATE

0

0

X

X

X

X

X

X

X

X

X

Shutdown Mode

1

0

0

X

X

X

X

X

X

X

X

Software-Shutdown Mode

1

0

1

X

X

X

X

X

X

X

X

Transmit-Disable Mode

1

1

1

X

X

X

X

X

X

X

X

Transmit Mode

1

1

1

X

0

0

0

0

0

0

0

Gain = -32dB*

1

1

1

X

0

0

0

0

0

1

1

Gain = -31dB*

1

1

1

X

—

—

—

—

—

—

—

—

1

1

1

X

1

0

0

0

0

0

32

Gain = 0dB*

1

1

1

X

—

—

—

—

—

—

—

—

1

1

1

X

1

1

1

1

1

0

62

Gain = 29dB*

1

1

1

X

1

1

1

1

1

1

63

Gain = 30dB*

*Typical gain at +25°C and VCC = +5V

Applications Information

Output Match

The MAX3510’s output circuit is an open-collector dif-

ferential amplifier. An on-chip resistor across the collec-

tors provides a nominal output impedance of 300Ω in

transmit mode and transmit disable mode.

Transformer

To match the output of the MAX3510 to a 75Ω load, a

2:1 (voltage ratio) transformer is required. This trans-

former must have adequate bandwidth to cover the

intended application. Note that most RF transformers

specify bandwidth with a 50Ω source on the primary

and a matching resistance on the secondary winding.

Operating in a 75Ω system will tend to shift the low-fre-

quency edge of the transformer bandwidth specifica-

tion up by a factor of 1.5, due to primary inductance.

Keep this in mind when specifying a transformer.

Bias to the output stage is provided through the center

tap on the transformer primary. This greatly diminishes

the on/off transients present at the output when switch-

ing between transmit and transmit-disable modes.

Commercially available transformers typically have

adequate balance between half-windings to achieve

substantial transient cancellation.

Finally, keep in mind that transformer core inductance

varies proportionally with temperature. If the application

requires low temperature extremes (less than 0°C),

adequate primary inductance must be present to sus-

tain low-frequency output capability as temperatures

drop. In general this will not be a problem, as modern

RF transformers have adequate bandwidth.

Input Circuit

To achieve rated performance, the input of the

MAX3510 must be driven differentially with an appropri-

ate input level. The differential input impedance is

approximately 1.5kΩ. Most applications will require a

differential lowpass filter preceding the device. The fil-

ter design will dictate terminating impedance of a spec-

ified value. Place this load impedance across the

AC-coupled input pins (see Typical Operating Circuit).

The MAX3510 has sufficient gain to produce an output

level of 60dBmV (CW through a 2:1 transformer) when

driven with a 34dBmV input signal. Rated performance

is achieved with this input level. When a lower input

level is present, the maximum output level will be

reduced proportionally and output linearity will

increase. If an input level greater than 34dBmV is used,

the 3rd-order distortion performance will degrade

slightly.

If a single-ended source drives the MAX3510, one of the

input terminals must be capacitively coupled to ground

(VIN+ or VIN-). The value of this capacitor must be

large enough to look like a short circuit at the lowest

frequency of interest. For operation at 5MHz with a 75Ω

source impedance, a value of 0.1µF will suffice.

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