LTC5586 datasheet(22/34 Pages) LINER

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LTC5586

5586fa

For more information www.linear.com/LTC5586

applicaTions inForMaTion

Interstage Filter

An interstage IF filter should be used between the MIP

(MIM) and AIP (AIM) pins and the MQP (MQM) and AQP

(AQM) pins to suppress the large fRF + fLO and other mix-

ing products from the mixer outputs. Without the filter, the

linearity of the amplifier can be degraded for the desired

signal. Figure 11 shows a recommended lowpass filter.

Table 4 shows typical values used for a lowpass response

of various bandwidths.

Table 4. Component Values for Interstage Lowpass Filter

1dB BW (MHz)

L1, L2 (nH)

C9, C11 (pF)

C10, C12 (pF)

330

120

150

100

300

4.7

6.8

500

3.0

1000

0.5

1.0

It is important that the placement of C10 and C12 be

as close as possible to the amplifier inputs. Long line

lengths on the amplifier inputs can lead to instability. As

shown in Figure 12, a 50Ω common-mode termination

resistor can be used to better ensure stability with long

line lengths and/or higher order filtering. The placement

of C9 and C11 should be as close as possible to the mixer

outputs for effective filtering of the 2xLO, fRF + fLO, and

other mixing products.

By adjusting the values of the capacitors in the filter, it

is possible to add or remove frequency slope of the IF

1pF

42mA

1.5nH

0.2pF

100

0.6pF

100

0.6pF

C11

C12

C10

LTC5586

AC CURRENT

SOURCE

PACKAGE

PARASITICS

1.5nH

0.2pF

PACKAGE

PARASITICS

VCC

GND

MIP

MIM

AIM

AIP

5586 F11

1pF

VCC

Figure 11. Simplified Schematic of the Mixer Output and IF Amplifier Input with Interstage Filter

Figure 12. Interstage IF Filter with Common-Mode Termination

C11

C12

C10

MIP

MIM

AIM

AIP

5586 F12

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