LTC6948 datasheet(16/26 Pages) AD

16 / 26 page

LTC5556

Rev 0

For more information www.analog.com

APPLICATIONS INFORMATION

LO Input

A simplified schematic of the LO input is shown in Figure 5.

As shown, each mixer has its own LO amplifier. A differen-

tial input is provided although the IC is characterized and

production-tested with single-ended drive. Differential LO

drive improves performance slightly, and is recommended

if available. Each LO input is internally matched to 50Ω

from 500MHz to 8GHz, requiring no external components.

ESD protection diodes on each input limit the peak volt-

age swing to approximately ±700mV (+7dBm), although

higher LO drive, up to 10dBm will not damage the input.

An external DC-blocking capacitor is only needed if the LO

source has DC voltage present. The measured LO input

return loss is shown in Figure 6.

Figure 5. LO Input Schematic

Figure 6. LO Input Return Loss

IF Outputs

A simplified IF output schematic for channel 1, with exter-

nal matching components is shown in Figure 7 (chan-

nel 2 is identical, and not shown). The final output stage

is differential, open-collector with integrated matching

resistors, capacitors and ESD protection diodes. Each

output pin must be biased at the supply voltage (VCC)

using external chokes (L11 and L13). Each pin draws

approximately 47mA of DC supply current (94mA total).

Therefore, inductors with low DC resistance (<1Ω), are

required for the highest output IP3 and P1dB.

The integrated output resistors set the differential output

resistance at 206Ω. C3, L15 and L17 form a 2:1 imped-

ance transformer which transforms the output to 100Ω

differential. If a 200Ω output is desired, C3 is not used

and the values of L15 and L17 are reduced to the values

shown in Table 1. C9 and C11 are DC-blocking capacitors,

which may be omitted if the following stage is already

DC-blocked.

Figure 7. IF Output Schematic

5556 F05

CH 1 MIX

LO–

LO+

(0dBm)

BLOCK

CH 2 MIX

–

5556 F07

IF1+

L11

L13

L15

IF1OUT

C11

L17

IF1–

VCC

TC = 25°C

NO EXTERNAL MATCH

LO FREQUENCY (GHz)

–18

–15

–12

–9

–6

–3

5556 F06

LTC6948 Datasheet(PDF) 16 Page - Analog Devices

LTC6948 Datasheet(HTML) 16 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL