LT5522

10

5522fa

RF FREQUENCY(GHz)

0.2

0

–5

–10

–15

–20

–25

–30

1.7

2.7

5522 F05

0.7

1.2

2.2

3.2

3.7

NO EXTERNAL

MATCH

C5 = 2.2pF

(900MHz)

L3 = 3.9nH

(HIGH BAND)

C5 = 8.2pF

L = 5mm

(450MHz)

APPLICATIO S I FOR ATIO

Introduction

The LT5522 consists of a high linearity double-balanced

mixer, RF buffer amplifier, high speed limiting LO buffer

amplifier and bias/enable circuits. The IC has been opti-

mized for downconverter applications where the RF input

signal is in the 400MHz to 2.7GHz range and the LO signal

is in the 400MHz to 2.7GHz range. Operation over a wider

RF input frequency range is possible with reduced

performance.

The IF output can be matched for IF frequencies as low as

100kHz or as high as 1GHz. The RF, LO and IF ports are all

differential, although the RF and LO ports are internally

matched for single-ended drive as shown in Figure 2. The

LT5522 is characterized and production-tested with single-

ended RF and LO drive. Low side or high side LO injection

can be used.

Two evaluation boards are available. The standard board

is intended for most applications, including cellular, PCS,

UMTS and 2.4GHz. A schematic is shown in Figure 2 and

the board layout is shown in Figure 18. The 140MHz IF

output frequency on the standard board is easily changed

by modifying the IF matching elements. The second board,

intended for CATV applications, incorporates a wideband

IF output balun. The CATV evaluation schematic is shown

in Figure 3 and the board layout is shown in Figure 19.

RF Input Port

The mixer’s RF input, shown in Figure 4, consists of an

integrated balun and a high linearity differential amplifier.

The primary terminals of the balun are connected to the

ary side of the balun is internally connected to the amplifier’s

although the LO to RF isolation will degrade slightly.

The RF source must be AC-coupled since one terminal of

the balun’s primary is grounded. If the RF source has DC

voltage present, then a coupling capacitor must be used in

series with the RF input pin.

As shown in Figure 5, the RF input return loss, with no

external matching, is greater than 10dB from 1.2GHz to

2.4GHz. The RF input match can be shifted down in

frequency by adding a shunt capacitor at the RF input. Two

examples are plotted in Figure 5. A 2.2pF capacitor,

located near Pin 3, produces a 900MHz match. An 8.2pF

capacitor, located 5mm away from Pin 3 (on the 50

Ω line),

produces a 450MHz match. The RF input match can also

be shifted up in frequency by adding a shunt inductor near

Pin 3. One example is plotted in Figure 5, where a 3.9nH

inductor produces a 2.3GHz to 2.8GHz match.

2

LT5522

3

RF IN

C5

OPTIONAL SHUNT

REACTANCE

FOR LOW BAND

OR HIGH BAND

MATCHING (C5 OR L3)

TO

MIXER

5522 F04

Figure 4. RF Input Schematic

Figure 5. RF Input Return Loss