LTC5541IUH データシートの表示（PDF） - Linear Technology

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LTC5541IUH

1.3GHz to 2.3GHz High Dynamic Range Downconverting Mixer

Linear Technology 

LTC5541

APPLICATIONS INFORMATION

Introduction

The LTC5541 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.

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. A broadband input match is realized with

C1 = 2.2pF. The measured input return loss is shown in

Figure 4 for LO frequencies of 1.4GHz, 1.75GHz and 2GHz.

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, although a single value of C1 is adequate to

cover the 1.3GHz-2.3GHz RF band.

5541 F02

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, is 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

is LO frequency-dependent and is not required for most

10

RFIN C1

RF

2

TO MIXER

CT

3

C2

LTC5541

5541 F03

Figure 3. RF Input Schematic

0

–5

LO = 2GHz

–10

–15

–20

–25

–30

1.0

LO = 1.4GHz

LO = 1.75GHz

1.5

2.0

2.5

FREQUENCY (GHz)

3.0

5541 F04

Figure 4. RF Input Return Loss

5541f

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