LT5506

10

5506fa

APPLICATIO S I FOR ATIO

which can occur during the gain settling. It also helps to

reduce the high frequency spectral content at the I/Q

outputs during overload. The second order integrated

lowpass filters are used for filtering the down-converted

baseband signals for both the I channel and the Q channel.

They serve as antialiasing and pulse-shaping filters. The

I/Q filters are well matched in gain response and group

delay. The 3dB corner frequency is typically 8.8MHz with

a group delay ripple of 5ns. The I/Q outputs can drive 2k

Ω

in parallel with a maximum capacitive loading of 10pF,

from all four pins to ground. The outputs are internally

output circuit schematic of the I channel or Q channel.

The I/Q baseband outputs can be DC-coupled to the inputs

of a baseband chip. For AC-coupled applications with large

capacitors, the STBY pin can be used to pre-bias the

This mode draws only 3.6mA supply current. When the EN

pin is then driven high (>1V), the chip is quickly switched

to normal operating mode, avoiding the introduction of

large charging time constants. Table 2 shows the logic of

Table 2. The Logic of Different Operating Modes

EN

STBY

Comments

Low

Low

Shutdown Mode

Low

High

Standby Mode

High

Low or High

Normal Operation Mode

Figure 5. Simplified Circuit Schematic of I Channel

(or Q Channel) Outputs and STBY (or EN) Input

300

µA

300

µA

I CHANNEL (OR

Q CHANNEL):

DIFFERENTIAL

SIGNALS

FROM LPF

+

–

5506 F05

STBY

(OR EN)

22k

the EN pin and STBY pin. In both normal operating mode

and standby mode, the maximum discharging current is

about 300

µA, and the maximum charging current is more

than 4mA. In Figure 5 the simplified circuit schematic of

the STBY (or EN) input is shown.

Figure 6. Evaluation Circuit Schematic with I/Q Output Buffers

–

+

1

2

3

4

12

11

10

9

STBY

EN

GND

GND

U1

LT5506

JTX-4-10T

MINI-CIRCUITS

R48

3.09k

R47

49.9

Ω

R51

100

Ω

C32

2.2pF

R40

3.09k

C29

2.2pF

R52

240

Ω

R36

20k

R35

20k

C34

0.1

µF

C35

4.7

µF

C38

0.1

µF

C37

0.1

µF

SW1

1 = EN

2 = STBY

1

6

1

6

–

+

C45

22nF

7

7

6

6

4

4

3

2

3

2

J1

OUT

OUT

OUT

–

OUT

OUT

OUT

–

J3

J4

C22

1

µF

C33

0.1

µF

C31

1

µF

R44

49.9

Ω

J2

C30

1

µF

U3

LT1809CS

U2

LT1809CS

C26

1.8pF

C25

1.5pF

C16

1nF

C15

1nF

C39

1

µF

C36

4.7

µF

R46

3.09k

R45

1k

C28

0.1

µF

R42

2k

R49

2k

R39

3.09k

R41

1k

R50

2k

C27

0.1

µF

R43

2k

2XLO

OVERLOAD

IF

DET

16

15

14

13

5

6

7

8

0

GND

NOTE: OUTPUT BUFFERS U2 AND U3 WITH ASSOCIATED

COMPONENTS ARE INCLUDED FOR MEASUREMENT PURPOSES ONLY.

BOARD NUMBER: DC468A (NARROW-BAND VERSION: DC535A)

C43, C45, C22, R51, C25, C26 AND C39 ARE OPTIONAL

5506 F04

JTX-4-10T

MINI-CIRCUITS

C43

22nF