lt5521 Linear Technology Corporation, lt5521 Datasheet - Page 14

• Manufacturer Part Number: lt5521
• Description: Very High Linearity Active Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5521
noise performance with slightly reduced current through
the mixer core. Accordingly, in a 5V application operating
within this LO frequency range, the recommended source
resistor value (R1 and R7) is increased to 121 .
Enable Interface
Figure 14 shows a simplified schematic of the EN pin
interface. The voltage necessary to turn on the LT5521 is
2.9V. To disable the chip, the enable voltage must be below
0.2V. If the EN pin is not connected, the chip is disabled.
It is not recommended, however, that any pins be left
floating for normal operation.
It is important that the voltage at the EN pin never exceed
V
should occur, the supply current could be sourced through
the EN pin ESD protection diodes, potentially damaging
the IC. The resistor R8 (Figure 1) in series with the EN pin
on the demo board is populated with a 10k resistor to
protect the EN pin to avoid inadvertant damage to the IC.
For timing measurements, this resistor is replaced with a
14
CC
, the power supply voltage, by more than 0.2V. If this
–10
–15
–20
–25
–30
–35
–5
0
0
Figure 14. Enable Input Circuit
Figure 13. LO Port Return Loss
500
U
C1 = 2.7pF
1000
LT5521
C1 = 6.8pF
V
FREQUENCY (MHz)
CC
1500
U
2000
2500
5
EN
3000
W
5521 F14
3500
5521 F13
4000
U
0 resistor. If the shutdown function is not required, then
the EN pin should be wired directly to the V
on the PCB.
Supply Decoupling
The power supply decoupling shown in the schematic of
Figure 1 is recommended to minimize spurious signal
coupling into the output through the power supply.
ACPR Performance
Because of its high linearity and low noise, the LT5521 offers
outstanding ACPR performance in a variety of applications.
For example, Figures 15 and 16 show ACPR and Alternate
Channel measurements for single channel and 4-channel
64 DPCH W-CDMA signals at 1.95GHz output frequency.
–100
Figure 15. Single Channel W-CDMA ACPR
and 30MHz Offset Noise Performance
–30
–40
–50
–60
–70
–80
–90
–50
–55
–60
–65
–70
–75
–80
Figure 16. 4-Channel W-CDMA ACPR,
AltCPR and 30MHz Offset Noise Floor
OUTPUT CHANNEL POWER, EACH CHANNEL (dBm)
–40
–40
T
f
f
f
T
f
f
f
RF
IF
LO
A
RF
IF
LO
A
= 70MHz
= 25 C
= 70MHz
= 1.95GHz
= 25 C
= 1.88GHz
= 1.95GHz
= 1.88GHz
OUTPUT CHANNEL POWER (dBm)
–35
–30
–30
30MHz OFFSET NOISE
–20
30MHz OFFSET NOISE
ACPR
AltCPR
–25
–10
ACPR
–20
0
5521 F15
–15
1635 G24
CC
10
–130
–135
–140
–145
–150
–155
–160
–165
–135
–140
–145
–150
–155
–160
–165
power supply
5521f