Rainbow-electronics CLC5957 Instrukcja Użytkownika Pobierz pdf (Strona 14)

CLC5957 Applications

Analog Inputs and Bias

Figure 1

depicts the analog input and bias scheme. Each of

the differential analog inputs are internally biased to a nomi-

nal voltage of 2.40V DC through a 500Ω resistor to a low

impedance buffer. This enables a simple interface to a

broadband RF transformer with a center-tapped output wind-

ing that is decoupled to the analog ground. If the application

requires the inputs to be DC coupled, the V

output can be

used to establish the proper common-mode input voltage for

the ADC. The V

voltage reference is generated from an

internal bandgap source that is very accurate and stable.

The V

output may also be used to power down the ADC.

When the V

pin is pulled above 3.5V, the internal bias

mirror is disabled and the total current is reduced to less than

10mA.

Figure 2

depicts how this function can be used. The

diode is necessary to prevent the logic gate from altering the

ADC bias value.

ENCODE Clock Inputs

The CLC5957’s differential input clock scheme is compatible

with all commonly used clock sources. Although small differ-

ential and single-ended signals are adequate, for best aper-

ture jitter performance a low noise differential clock with a

high slew rate is preferred. As depicted in

Figure 3

, both

ENCODE clock inputs are internally biased to V

/2 through

a pair of 5kΩ resistors. The clock input buffer operates with

any common-mode voltage between the supply and ground.

The internal bias resistors simplify the clock interface to

another center-tapped transformer as depicted in

Figure 4

low phase noise, RF synthesizer of moderate

amplitude (1 − 4V

) can drive the ADC through this inter-

face.

Figure 5

shows the clock interface scheme for square wave

clock sources.

015029F1

FIGURE 1. CLC5957 Bias Scheme

015029F2

FIGURE 2. Power Shutdown Scheme

015029F3

FIGURE 3. CLC5957 ENCODE Clock Inputs

015029F4

FIGURE 4. Transformer Coupled Clock Scheme

015029F5

FIGURE 5. TTL, 3V CMOS or 5V CMOS Clock Scheme

CLC5957

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