lt5554 Linear Technology Corporation, lt5554 Datasheet - Page 21

• Manufacturer Part Number: lt5554
• Description: Broadband Ultra Low Distortion 7-bit Digitally Controlled Vga
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Gain Step Accuracy
LT5554 internal input signal coupling to the transcon-
ductance amplifi er inputs across the 4dB step attenuator
increases with frequency. The gain step error is higher
when the LT5554 gain update changes the input attenua-
tor tap (PG5, PG6 transitions) and this error is frequency
dependent.
Gain error is ‘compressive’, effectively reducing LT5554
gain range. Therefore, it is possible to skip one gain
Figure 12. Linearity, 70MHz, R
Figure 10. Noise, 140MHz, R
–70
–74
–78
–82
–86
12
9
6
3
0
0
0
V
ONOISE
NF
RTI
–4
–4
ATTENUATION (dB)
ATTENUATION (dB)
OIP3
IMD3
–8
–8
OUT
–12
= 50Ω, 4dBm/Tone
–12
OUT
= 50Ω
5554 F10
5554 F12
–16
–16
24
18
12
6
0
48
46
44
42
40
code whenever PG5, PG6 transitions are involved in or-
der to preserve high-frequency monotonic behavior for
0.125dB steps.
Linearity and Noise Performance Throughout the
Gain Range
The LT5554’s Noise and Linearity performance across
the 16dB gain range at 100MHz with R
R
SADC
Figure 13. Linearity, 140MHz, R
= 50Ω is shown in Figures 10 through 13.
Figure 11. Noise, 140MHz, R
–70
–74
–78
–82
–86
44
39
34
29
24
0
0
SFDR
IIP3
–4
–4
ATTENUATION (dB)
ATTENUATION (dB)
OIP3
IMD3
–8
–8
OUT
–12
–12
= 50Ω, 4dBm/Tone
OUT
= 50Ω
5554 F11
5554 F12
OUT
–16
–16
LT5554
48
46
44
42
40
136
132
128
124
120
= 100 and
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