LTC5542 데이터 시트보기 (PDF) - Linear Technology

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LTC5542

1.6GHz to 2.7GHz High Dynamic Range Downconverting Mixer

Linear Technology 

LTC5542

APPLICATIONS INFORMATION

Introduction

The LTC5542 consists of a high linearity passive double-

balanced mixer core, IF buffer amplifier, high speed single-

pole double-throw (SPDT) LO switch, LO buffer amplifier

and bias/shutdown circuits. See Block Diagram section for

a description of each pin function. The RF and LO inputs

are single-ended. The IF output is differential. Low-side or

high-side LO injection can be used. The evaluation circuit,

shown in Figure 1, utilizes bandpass IF output matching and

an IF transformer to realize a 50Ω single-ended IF output.

The evaluation board layout is shown in Figure 2.

is LO frequency-dependent and is not required for most

applications. When used, C2 should be located within

2mm of pin 3 for proper high-frequency decoupling. The

nominal DC voltage on the CT pin is 1.2V.

For the RF input to be matched, the selected LO input must

be driven. The measured RF input return loss is shown

in Figure 4 for LO frequencies of 1.7GHz, 2.1GHz and

2.5GHz. These LO frequencies correspond to the lower,

middle and upper values of the LO range. As shown in

Figure 4, the RF input impedance is somewhat dependent

on LO frequency.

55554412 FF0022

Figure 2. Evaluation Board Layout

RF Input

The mixer’s RF input, shown in Figure 3, is connected to

the primary winding of an integrated transformer. A 50Ω

match is realized when a series capacitor C1 and shunt

capacitor C11, are connected to the RF input. C1 is also

needed for DC blocking if the RF source has DC voltage

present, since the primary side of the RF transformer is

DC-grounded internally. The DC resistance of the primary

is approximately 3.6Ω.

The secondary winding of the RF transformer is internally

connected to the passive mixer. The center-tap of the

transformer secondary is connected to pin 3 (CT) to allow

the connection of bypass capacitor, C2. The value of C2

10

RFIN C1

RF

2

C11

CT

3

C2

TO MIXER

LTC5542

5542 F03

Figure 3. RF Input Schematic

0

LO = 2.5GHz

C1 = 22pF

C11 = 0.7pF

–5

LO = 2.1GHz

–10

LO = 1.75GHz

–15

–20

–25

–30

1.2

1.7

2.2

2.7

FREQUENCY (GHz)

3.2

5542 F04

Figure 4. RF Input Return Loss

5542f

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