lt5560 Linear Technology Corporation, lt5560 Datasheet - Page 21

• Manufacturer Part Number: lt5560
• Description: 0.01mhz To 4ghz Low Power Active Mixer
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Enable Interface
Figure 12 shows a simplifi ed schematic of the EN pin
interface. The voltage necessary to turn on the LT5560 is
2V. To disable the chip, the enable voltage must be less
than 0.3V. If the EN pin is allowed to fl oat, the chip will tend
to remain in its last operating state, thus it is not recom-
mended that the enable function be used in this manner.
If the shutdown function is not required, then the EN pin
should be connected directly to V
The voltage at the EN pin should never exceed the power
supply voltage (V
occur, the supply current could be sourced through the
EN pin ESD diode, potentially damaging the IC.
Adjustable Supply Current
The LT5560 offers a direct trade-off between power sup-
ply current and linearity. This capability allows the user
to optimize the performance and power dissipation of
the mixer for a particular application. The supply current
can be adjusted by changing the value of resistor R1 at
the center-tap of the input balun. For downconversion
applications, a bypass capacitor in parallel with R1 may
be desired to minimize noise fi gure. The bypass capacitor
has a greater effect on noise fi gure at larger values of R1.
In upmixer confi gurations, adding a capacitor across R1
has little effect.
Figure 13 shows the supply current as a function of R1.
Note that the current will also be affected by parasitic
resistance in the matching components. Figure 14 il-
lustrates the effect of supply current on Gain, IIP3 and
NF of a 900MHz upconverting mixer. The performance
Figure 12. Enable Input Circuit
2
EN
CC
U
) by more than 0.3V. If this should
V
CC
U
LT5560
CC
60k
W
5560 F12
.
U
vs current of a 900MHz downconverting mixer is plotted
in Figure 15. In this example, a 1nF capacitor has been
placed in parallel to R1 for best noise fi gure.
Figure 15. 900MHz Downconverting Mixer Gain,
Noise Figure and IIP3 vs Supply Current
Figure 13. Typical Supply Current vs R1 Value
Figure 14. 900MHz Upconverting Mixer Gain,
Noise Figure and IIP3 vs Supply Current
14
13
12
11
10
–2
–2
14
12
10
14
12
10
9
8
7
4
6
5
6
4
2
6
4
2
8
0
8
0
0
4
4
MEASURED WITH InF CAP ACROSS R1
T
V
A
CC
SSB NF
SSB NF
= 25°C
= 3V
5
IIP3
6
6
IIP3
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
10
T
V
f
8
T
V
f
8
LO
LO
A
A
CC
CC
R1 (Ω)
= 25°C
= 25°C
= 760MHz
15
= 760MHz
= 3V
= 3V
10
10
GAIN
GAIN
20
f
P
f
P
IF
IF
LO
LO
= 140MHz
= 140MHz
12
12
= –2dBm
= –2dBm
25
5560 F14
5560 F15
5560 F13
30
14
14
LT5560
21
5560f