LT5514 datasheet(13/20 Pages) LINER

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LT5514

5514f

Input Interface

For the lowest noise and highest linearity, the LT5514

should be driven with a differential input signal. Single-

ended drive will severely degrade linearity and noise

performance.

Example input matching networks are shown in Figures 3

and 4.

Input matching network design criteria are:

• DC block the LT5514 internal bias voltage (see Input

Bias Voltage section for DC coupling information)

• Match the source impedance to the LT5514, RIN ≅ 108Ω

• Provide well balanced differential input drive (capacitor

C2 in Figure 4)

• Minimize insertion loss to avoid degrading the noise

figure (NF)

Note: In Figure 5, (choke) inductors may be placed in

parallel with or used to replace resistors R1 and R2, thus

eliminating the DC voltage drop across these resistors.

APPLICATIO S I FOR ATIO

–

RIN

100

Ω

IN+

VSRC

LT5514

LT5514 F03

Ω

IN–

Figure 3. Input Capacitively-Coupled to a Differential Source

–

RIN

100

Ω

IN+

0.33

µF

LT5514

LT5514 F04

RSRC

Ω

1:2

•

VSRC

IN–

Figure 4. Input Transformer-Coupled to a Single-Ended Source

Output Interface

The output interface network provides an impedance

transformation between the actual load impedance, RLOAD,

and the LT5514 output loading, ROUT, chosen to maximize

power or linearity, or to minimize output noise, or for some

other criteria as explained in the following sections.

Two examples of output matching networks are shown in

Figures 5 and 6 (as implemented in the LT5514 demo

boards).

Figure 5. Output Impedance-Matched

and Capacitively Coupled to a Differential Load

–

RIN

100

Ω

IN+

LT5514

Ω

VOSUP

RLOAD

Ω

RLOAD

Ω

ROUT

LT5514 F05

IN–

Figure 6. Output Impedance-Matched and

Transformer-Coupled to a Single-Ended Load

–

RIN

100

Ω

IN+

LT5514

RMATCH

255

Ω

(OPTIONAL)

VOSUP

RLOAD

Ω

4:1

ROUT

LT5514 F06

IN–

•

Output network design criteria are:

• Provide DC isolation between the LT5514 DC output

voltage and RLOAD.

• Provide a path for the output DC current from the output

voltage source VOSUP.

• Provide an impedance transformation, if required, be-

tween the load impedance, RLOAD, and the optimum

ROUT loading.

• Set the bandwidth of the output network.

• Optional: Provide board output impedance matching

using resistor RMATCH (when driving a transmission

line).

• Use high linearity passive parts to avoid introducing

noninearity.

Note that there is a noise penalty of up to 6dB when using

power delivered by only one output in Figure 5.

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