LTC5591 datasheet(13/20 Pages) LINER

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LTC5592

5592f

Introduction

The LTC5592 consists of two identical mixer channels

driven by a common LO input signal. Each high linearity

mixer consists of a passive double-balanced mixer core,

IF buffer amplifier, LO buffer amplifier and bias/enable

circuits. See the Pin Functions and Block Diagram sections

for a description of each pin. Each of the mixers can be

shutdown independently to reduce power consumption and

low current mode can be selected that allows a trade-off

between performance and power consumption. The RF and

LO inputs are single-ended and are internally matched to

50Ω. Low side or high side LO injection can be used. The

IF outputs are differential. 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 INFORMATION

Figure 2. Evaluation Board Layout (DC1710A)

The secondary winding of the RF transformer is inter-

nally connected to the channel A passive mixer core. The

center-tap of the transformer secondary is connected to

Pin 2 (CTA) to allow the connection of bypass capacitor,

C8A. The value of C8A can be adjusted to improve channel

isolation at specific RF frequencies with minor impact to

conversion gain, linearity and noise performance. When

used, it should be located within 2mm of Pin 2 for proper

high frequency decoupling. The nominal DC voltage on

the CTA pin is 1.2V.

For the RF inputs to be properly matched, the appropriate

LO signal must be applied to the LO input. A broadband

input match is realized with C1A = 22pF. The measured

input return loss is shown in Figure 4 for LO frequencies

of 1.7GHz, 2.16GHz and 2.5GHz. These LO frequencies

correspond to lower, middle and upper values in the LO

range. As shown in Figure 4, the RF input impedance is

dependent on LO frequency, although a single value of

C1A is adequate to cover the 1.7GHz to 2.5GHz RF band.

RF Inputs

The RF inputs of channels A and B are identical. The RF

input of channel A, shown in Figure 3, is connected to the

primary winding of an integrated transformer. A 50Ω match

is realized when a series external capacitor, C1A, is con-

nected to the RF input. C1A is also needed for DC blocking

if the source has DC voltage present, since the primary

side of the RF transformer is internally DC-grounded. The

DC resistance of the primary is approximately 3.9Ω.

Figure 3. Channel A RF Input Schematic

Figure 4. RF Port Return Loss

5592 F02

LTC5592

C1A

C8A

RFA

CTA

RFA

TO CHANNEL A

MIXER

5592 F03

FREQUENCY (MHz)

1500

–25

–20

–15

–10

–5

1700

5592 F04

1900

2100

2300

2500

2700

LO = 1700MHz

LO = 2160MHz

LO = 2500MHz

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