LTC5585_15 datasheet(21/38 Pages) LINER

21 / 38 page

LTC5585

5585fb

For more information www.linear.com/LTC5585

APPLICATIONS INFORMATION

tone spacing is 1MHz, and fLO is 10MHz lower than fRF.

The conversion gain is lower than under the impedance

matched condition, and correspondingly the P1dB, IIP3,

and NF are higher. As shown, the part can be used at

frequencies outside its specified operating range with

reduced conversion gain and higher NF.

LO Input Port

The demodulator’s LO input interface is shown in Fig-

ure 12. The input consists of a high precision quadrature

phase shifter which generates 0° and 90° phase shifted

LO signals for the LO buffer amplifiers to drive the I/Q

mixers. DC blocking capacitors are required on the LO+

and LO– inputs.

Figure 8. Broadband IIP3 and IP1dB

Figure 11. Broadband Image Rejection

Figure 9. Broadband IIP2

Figure 10. Broadband NF and Gain

ThedifferentialLOinputimpedanceandSparameterswith

the input transmission lines and balun de-embedded are

listed in Table 2.

Figure 13 shows LO input return loss using the ANAREN

BD0826J50200A00 4:1 balun with various matching

component values.

For optimum IIP2 and large-signal NF performance the LO

inputs should be driven differentially with a 4:1 balun such

astheANARENBD0826J50200A00orBD2425J50200AHF.

As shown in Figure 14, the LO input can also be driven

single-ended from either the LO+ or LO– input. The unused

portshouldbeDC-blockedandterminatedwitha50Ωload.

Figure 15 compares the uncalibrated IIP2 performance of

single ended versus differential LO drive.

LO FREQUENCY (MHz)

400

1400

2400 2900 3400

5585 F08

900

1900

3900

I, –40°C

I, 25°C

I, 85°C

I, 105°C

Q, –40°C

Q, 25°C

Q, 85°C

Q, 105°C

IIP3

P1dB

LO FREQUENCY (MHz)

400

130

100

1400

2400 2900 3400

5585 F09

110

120

900

1900

3900

I, –40°C

I, 25°C

I, 85°C

I, 105°C

Q, –40°C

Q, 25°C

Q, 85°C

Q, 105°C

LO FREQUENCY (MHz)

–4

–2

1400

2400 2900 3400

5585 F10

900

1900

3900

I, –40°C

I, 25°C

I, 85°C

I, 105°C

Q, –40°C

Q, 25°C

Q, 85°C

Q, 105°C

GAIN

LO FREQUENCY (MHz)

500

4000

5585 F11

1500

2500

3500

1000

2000

3000

100

TC = –40°C

TC = 25°C

TC = 85°C

TC = 105°C

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