LT5557EUF#TRPBF Datasheet LT5557EUF#PBF, LT5557EUF#TRPBF | P10-P12

LT5557

5557fc

applicaTions inForMaTion

This series transmission line/shunt capacitor matching to-

pology allows the LT5557 to be used for multiple frequency

standards without circuit board layout modifications. The

series transmission line can also be replaced with a series

chip inductor for a more compact layout.

Input return losses for the 450MHz, 900MHz, 2.6GHz

and 3.6GHz applications are plotted in Figure 4b. The

input return loss with no external matching is repeated

in Figure 4b for comparison. The 2.6GHz RF input match

uses the highpass matching network shown in Figures 1

and 3 with C5 = 3.9pF and L5 = 3.6nH. The highpass in-

put matching network is also used to create a wideband

or dual-band input match. For example, with C5 = 3.3pF

and L5 = 10nH, the RF input is matched from 800MHz to

2.2GHz, with optimum matching in the 800MHz to 1.1GHz

and 1.6GHz to 2.2GHz bands, simultaneously.

RF input impedance and S11 versus frequency (with no

external matching) are listed in Table 1 and referenced

to Pin 3. The S11 data can be used with a microwave

circuit simulator to design custom matching networks

and simulate board level interfacing to the RF input filter.

Table 1. RF Input Impedance vs Frequency

FREQUENCY

(MHz)

INPUT

IMPEDANCE

S11

MAG ANGLE

50 4.6 + j2.3 0.832 174.7

300 9.1 + j11.2 0.706 153.8

450 12.0 + j14.5 0.639 145.8

600 14.7 + j17.4 0.588 138.7

900 20.5 + j23.3 0.506 123.4

1300 34.4 + j30.3 0.380 97.5

1700 59.6 + j23.8 0.229 55.8

1950 69.2 + j2.8 0.163 6.9

2200 59.2 – j18.1 0.184 –53.5

2450 41.5 – j24.5 0.274 –94.2

2700 28.3 – j21.3 0.374 –120.3

3000 19.0 – j13.5 0.481 –145.5

3300 13.9 – j5.1 0.568 –167.3

3600 10.8 + j3.4 0.645 171.9

3900 9.4 + j12.3 0.700 151.4

LO Input Port

The mixer’s LO input, shown in Figure 5, consists of an

integrated transformer and high speed limiting differential

amplifiers. The amplifiers are designed to precisely drive

the mixer for the highest linearity and the lowest noise

figure. An internal DC blocking capacitor in series with the

transformer’s primary eliminates the need for an external

blocking capacitor.

The LO input is internally matched from 1GHz to 5GHz.

The input match can be shifted down, as low as 750MHz,

with a single shunt capacitor (C4) on Pin 15. One exam-

ple is plotted in Figure 6 where C4 = 2.7pF produces a

750MHz to 1GHz match.

LO input matching below 750MHz requires the series

inductor (L4)/shunt capacitor (C4) network shown in

Figure 5. Two examples are plotted in Figure 6, where L4

= 2.7nH/C4 = 3.9pF produces a 650MHz to 830MHz match

and L4 = 10nH/C4 = 8.2pF produces a 460MHz to 560MHz

match. The evaluation boards do not include pads for L4,

so the circuit trace needs to be cut near Pin 15 to insert

L4. A low cost multilayer chip inductor is adequate for L4.

Figure 5. LO Input Schematic

Figure 6. LO Input Return Loss

CC2

LIMITER

REF

5557 F05

EXTERNAL

MATCHING

FOR LO < 1GHz

MIXER

REGULATOR

LO FREQUENCY (GHz)

0.3

L4 = 10nH

C4 = 8.2pF

L4 = 2.7nH

C4 = 3.9pF

L4 = 0

C4 = 2.7pF

–30

LO PORT RETURN LOSS (dB)

–10

1 5

5557 G06

–20

NO EXT

MATCH

LT5557

5557fc

applicaTions inForMaTion

The optimum LO drive is –3dBm for LO frequencies above

1.2GHz, although the amplifiers are designed to accom-

modate several dB of LO input power variation without

significant mixer performance variation. Below 1.2GHz,

0dBm LO drive is recommended for optimum noise figure,

although –3dBm will still deliver good conversion gain

and linearity.

Custom matching networks can be designed using the port

impedance data listed in Table 2. This data is referenced

to the LO pin with no external matching.

Table 2. LO Input Impedance vs Frequency

FREQUENCY

(MHz)

INPUT

IMPEDANCE

S11

MAG ANGLE

50 10.0 – j326 0.991 –17.4

300 8.5 – j41.9 0.820 –99.2

500 11.8 – j10.1 0.632 –155.9

700 18.8 + j10.9 0.474 151.8

900 35.0 + j27.4 0.350 100.8

1200 72.9 + j19.3 0.241 31.3

1500 70.0 – j12.6 0.196 –26.1

1800 55.0 – j17.0 0.167 –64.3

2200 47.8 – j9.7 0.102 –97.2

2600 53.6 – j1.9 0.039 –26.8

3000 66.7 + j0.7 0.143 2.1

3500 82.1 – j13.9 0.263 –17.4

4000 69.0 – j30.1 0.290 –43.5

4500 43.7 – j13.2 0.154 –107.5

5000 36.4 + j19.8 0.271 111.6

IF Output Port

The IF outputs, IF

and IF

–

, are internally connected to the

collectors of the mixer switching transistors (see Figure 7).

Both pins must be biased at the supply voltage, which

can be applied through the center tap of a transformer or

through matching inductors. Each IF pin draws 26.6mA

of supply current (53.2mA total). For optimum single-

ended performance, these differential outputs should

be combined externally through an IF transformer or a

discrete IF balun circuit. The standard evaluation board

(see Figure 1) includes an IF transformer for impedance

transformation and differential to single-ended transfor-

mation. A second evaluation board (see Figure 2) realizes

the same functionality with a discrete IF balun circuit.

The IF output impedance can be modeled as 560Ω in

parallel with 2.6pF at low frequencies. An equivalent small-

signal model (including bondwire inductance) is shown

in Figure 8. Frequency-dependent differential IF output

impedance is listed in Table 3. This data is referenced

to the package pins (with no external components) and

includes the effects of IC and package parasitics. The IF

output can be matched for IF frequencies as low as several

kHz or as high as 600MHz.

Table 3. IF Output Impedance vs Frequency

FREQUENCY (MHz)

DIFFERENTIAL OUTPUT

IMPEDANCE (R

|| X

)

1 560 || – j63.7k (2.6pF)

70 556 || – j870 (2.6pF)

140 551 || – j440 (2.6pF)

190 523 || – j320 (2.6pF)

240 529 || – j254 (2.6pF)

300 509 || – j200 (2.66pF)

360 483 || – j163 (2.7pF)

450 448 || – j125 (2.83pF)

600 396 || – j92 (2.88pF)

Two methods of differential to single-ended IF matching

are described:

• Transformer-basedbandpass

• DiscreteIFbalun

Figure 7. IF Output with External Matching

Figure 8. IF Output Small-Signal Model

8:1

5557 F07

–

OUT

50Ω

0.7nH

5557 F08

–

|| X

LT5557

5557fc

applicaTions inForMaTion

Transformer-Based Bandpass IF Matching

The standard evaluation board (shown in Figure 1) uses

an L-C bandpass IF matching network, with an 8:1 trans-

former connected across the IF pins. The L-C network

maximizes mixer performance at the desired IF frequency.

The transformer performs impedance transformation and

provides a single-ended 50Ω output.

The value of L1 is calculated as:

L1 = 1/[(2πf

)

•C

]

where C

is the sum of C3 and the internal IF capacitance

(listed in Table 3). The value of C3 is selected such that L1

falls on a standard value, while satisfying the desired IF

bandwidth. The IF bandwidth can be estimated as:

= 1/(2πR

EFF

)

where R

EFF

, the effective IF resistance when loaded with

the transformer and inductor loss, is approximately 200Ω.

Below 40MHz, the magnitude of the internal IF reactance

is relatively high compared to the internal resistance. In

this case, L1 (and C3) can be eliminated, and the 8:1

transformer alone is adequate for IF matching.

The LT5557 was characterized with IF frequencies of

70MHz, 140MHz, 240MHz, 360MHz and 450MHz. The

values of L1 and C3 used for these frequencies are tabu-

lated in Figure 1 and repeated in Figure 9. In all cases,

L1 is a high-Q 0603 wire-wound chip inductor, for high-

est conversion gain. Low cost multilayer chip inductors

can be substituted, with a slight reduction in conversion

gain. The measured IF output return losses are plotted in

Figure 9.

Discrete IF Balun Matching

For many applications, it is possible to replace the IF

transformer with the discrete IF balun shown in Figure 2.

The values of L1, L2, C6 and C7 are calculated to realize

a 180 degree phase shift at the desired IF frequency and

provide a 50Ω single-ended output, using the following

equations. Inductor L3 is calculated to cancel the internal

2.6pF capacitance. L3 also supplies bias voltage to the IF

pin. Low cost multilayer chip inductors are adequate for

L1, L2 and L3. C3 is a DC blocking capacitor.

L1, L2 =

• R

OUT

C6,C7 =

• R

OUT

L3 =

Figure 9. IF Output Return Loss with

Transformer-Based Bandpass Matching

IF FREQUENCY (MHz)

A: 70MHz, L1 = 270nH, C3 = 15pF

B: 140MHz, L1 = 180nH, C3 = 3.9pF

C: 240MHz, L1 = 82nH, C3 = 2.2pF

D: 360MHz, L1 = 47nH, C3 = 1.2pF

E: 450MHz, L1 = 39nH, C3 = 0pF

–30

IF PORT RETURN LOSS (dB0

–20

–10

150 250 350 450

5557 G09

550

D E

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18

LT5557EUF#TRPBF

Mfr. #:

Buy LT5557EUF#TRPBF

Manufacturer:

Analog Devices Inc.

Description:

RF Mixer 400 MHz to 3.8 GHz 3.3V Downconverting Mixer

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LT5557EUF#TRPBF

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