LT5524EFE Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT5524EFE

Low Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain

Linear Technology 

LT5524

APPLICATIO S I FOR ATIO

bandwidth, but will also degrade linearity because part of

the available power is wasted driving the capacitive load.

The LT5524’s output reactance is capacitive. Therefore

improved AC response is possible by using external series

output inductors. When driving purely resistive loads, an

inductor in series with the LT5524 output may help to

achieve maximally flat AC response as exemplified in the

characterization setup schematic (Figure 9).

The series inductor can extend the application bandwidth,

but it provides no improvement in linearity performance.

Series inductance may also produce peaking in the AC

response. This can be the case when (high Q) choke

inductors are used in an output interface such as in

Figure 5, and the PCB trace (connection) to the load is too

long. Since the LT5524’s output impedance is relatively

high, the PCB trace acts as a series inductor. The most

direct solution is to shorten the connection lines by

placing the driver closer to the load. Another solution to

flatten the AC response is to place resistance close to the

LT5524 outputs. In this way the connection line behaves

more like a terminated transmission line, and the AC

peaking due to the capacitive load can be removed.

Bandpass Applications

For narrow band IF applications, the LT5524’s output

capacitance and the application load capacitance can be

incorporated as part of an LC impedance transformation

network, giving improved linearity performance for signal

frequencies greater than 100MHz. Figure 8 is an example

of such a network.

The network consists of two parallel resonant LC tank

circuits critically coupled by capacitors C1 and C2. The

ROUT to RLOAD transformation ratio in this particular

implementation is 2. The choice of impedance transfor-

mation ratio is more flexible than in the wideband case.

The LC network is a bandpass filter, a useful feature in

many applications.

A variety of bandpass matching network configurations

are conceivable, depending on the requirements of the

particular application. The design of these networks is

facilitated by the fact that the LT5524 outputs are not

destabilized by reactive loading.

Note that these LC networks may distort the output signal

if their amplitude and phase response exhibit nonlinear

behavior. For example, if resistors R1 and R2 in Figure 5

are replaced with LC resonant tank circuits, then severe

OIP3 degradation may occur.

Low Output Noise Floor Applications

In some applications the maximum output noise floor is

specified. The LT5524 output noise floor is elevated above

the available noise power (–174dBm/Hz into 50Ω) by the

NF + Gain. Consequently, reduction of the LT5524’s power

gain is the only way to reduce the output noise floor.

VCC

RSRC

50Ω

VSRC

C8

T1

0.1µF

1:2

TC2-1T

C9

0.33µF

PGA0 PGA1 PGA2 PGA3

LT5524

IN+ –

DUT

IN– +

ROUT

200Ω

GAIN = 27dB

L5

56nH

L6 C1

56nH 12pF

C6

2.2pF

C2

12pF

1dB BANDWIDTH:

fL = 130MHz

fU = 220MHz

NOTE:

C3 + CLOAD = 12pF

C4 + CLOAD = 12pF

C7

0.1µF

L3

C3

56nH

C5

5.6pF L4

56nH

RLOAD

100Ω

C4

VOSUP

RLOAD

50Ω

RLOAD

50Ω

5524 F08

Figure 8. Bandpass Output Transformation Network Example

CLOAD

CLOAD

5524f

12

Share Link: