MAX3532EAX Просмотр технического описания (PDF) - Maxim Integrated

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MAX3532EAX

Upstream CATV Driver Amplifier

Maxim Integrated 

Upstream CATV Driver Amplifier

Table 2. Chip-State Control Bits

TXEN

D7 D6 D5 D4 D3 D2 D1 D0

1

1

1

X

X

X

X

X

X

1

1

0

X

X

X

X

X

X

X

0

1

X

X

X

X

X

X

0*

X

X

X

0

0

X

X

X

X

X

X

1

1

0

0

0

1

1

0

1

1

1

0

0

0

1

1

1

0

—

1

—

—

—

—

—

—

—

1

1

1

1

1

0

1

0

1

1

1

1

1

1

0

1

1

0

*Except state 000XXXXXX, which is software shutdown.

STATE

High-power transmit

Low-noise transmit; subtract 16dB from VOUT

Transmit disabled

All analog circuitry off

VOUT = +8dBmV

VOUT = +9dBmV

—

VOUT = +56dBmV

VOUT = +57dBmV

A

B

C

DE

F

D7 D6 D5 D4 D3 D2 D1 D0

A: tCSS

B: tSDAS

C: tSDAH

D: tSCKL

E: tSCKH

F: tCSH

Figure 2. Serial-Interface Timing Diagram

Software Shutdown Mode

Software-shutdown mode is enabled when both D7 and

D6 are low (D7, D6 = 00). This mode minimizes current

consumption while maintaining the programmed gain

state stored in the serial data-interface’s latch. All ana-

log functions are disabled in this mode.

__________Applications Information

Output Match

The MAX3532’s output circuit is a differential emitter fol-

lower that has a near-zero impedance over the operat-

ing frequency range. In order to match to a single-

ended impedance, a transformer and back-termination

resistors are required. Furthermore, operation from a

single +5V supply requires that the output signal swing

be stepped up to achieve the rated output levels.

These are described in the next two sections.

Transformer

To achieve the rated output levels, a 1:2 (voltage ratio)

transformer is required. This transformer must have

adequate bandwidth to cover the intended application.

Note that most RF transformers specify a bandwidth

with a 50Ω load on the primary and a matching resis-

tance on the secondary winding. The much lower

(approximately 16Ω due to the back-termination resis-

tors) impedance of the MAX3532’s output will tend to

shift the low-frequency edge of the bandwidth specifi-

cation down by a factor of three or more due to primary

inductance. Keep this in mind when specifying a trans-

former.

RF transformer cores are inherently nonlinear devices,

which must be operated in their linear region if distor-

tion is a critical consideration. In general, the size of the

transformer core used and the number of turns will gov-

ern the distortion performance of the transformer for a

given output level. Therefore a transformer of adequate

size must be used to minimize its contribution to the

overall distortion budget.

Back-Termination Resistors

The value of the back-termination resistors depends on

two parameters: the ultimate output impedance (as

referred through the output transformer), and the quali-

ty of the output match desired. The output impedance

depends on the value of the termination resistors by the

following formula:

ZOUT = 4 x [ 2 x (Rterm + RP)]

where Rterm is the value of one termination resistor and

RP is parasitic resistance.

_______________________________________________________________________________________ 7

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