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

The IFBIAS pin (pin 20) is available for reducing the DC

current consumption of the IF amplifier, at the expense of

IIP3. This pin should be left open-circuited for optimum

performance. The internal bias circuit produces a 4mA

reference for the IF amplifier, which causes the amplifier

to draw approximately 100mA. If resistor R1 is connected

to pin 20 as shown in Figure 7, a portion of the reference

current can be shunted to ground, resulting in reduced

IF amplifier current. For example, R1 = 1kΩ will shunt

away 1.5mA from pin 20 and the IF amplifier current will

be reduced by 38% to approximately 62mA. The nominal,

open-circuit DC voltage at pin 20 is 2.1V. Table 6 lists RF

performance at 1950MHz versus IF amplifier current.

Table 6. Mixer Performance with Reduced IF Amplifier Current

(RF = 1950MHz, Low-Side LO, IF = 190MHz)

VCCIF =3.3V

R1

ICCIF

GC

IIP3

P1dB

NF

(kΩ)

(mA)

(dB)

(dBm) (dBm)

(dB)

OPEN

100

7.8

26.4

11.4

9.6

4.7

90

7.5

26.0

11.6

9.6

2.2

81

7.4

25.3

11.7

9.5

1

62

6.9

23.4

11.7

9.7

VCCIF = 5V

R1

(kΩ)

ICCIF

(mA)

GC

IIP3

P1dB

NF

(dB)

(dBm) (dBm)

(dB)

OPEN

102

7.7

27.3

14.6

9.7

4.7

92

7.5

27.2

14.7

9.6

2.2

83

7.2

26.5

14.8

9.6

1

65

6.7

24.7

14.0

9.7

Shutdown Interface

Figure 11 shows a simplified schematic of the SHDN pin

interface. To disable the chip, the SHDN voltage must be

higher than 3.0V. If the shutdown function is not required,

the SHDN pin should be connected directly to GND. The

voltage at the SHDN pin should never exceed the power

supply voltage (VCC) by more than 0.3V. If this should

occur, the supply current could be sourced through the

ESD diode, potentially damaging the IC.

The SHDN pin must be pulled high or low. If left floating,

then the on/off state of the IC will be indeterminate. If a

three-state condition can exist at the SHDN pin, then a

pull-up or pull-down resistor must be used.

VCC2

6

LTC5541

SHDN

5

500Ω

5541 F11

Figure 11. Shutdown Input Circuit

Supply Voltage Ramping

Fast ramping of the supply voltage can cause a current

glitch in the internal ESD protection circuits. Depending on

the supply inductance, this could result in a supply voltage

transient that exceeds the maximum rating. A supply voltage

ramp time of greater than 1ms is recommended.

5541f

14

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