LT5581IDDB#PBF Linear Technology, LT5581IDDB#PBF Datasheet - Page 14

• Manufacturer Part Number: LT5581IDDB#PBF
• Manufacturer: Linear Technology

Specifications of LT5581IDDB#PBF

• Pin Count: 8
• Screening Level: Industrial
• Lead Free Status / Rohs Status: Compliant

LT5581
Figure 10 shows that rise time and fall time are strong
functions of RF input power. Data is taken without the
output fi lter capacitor.
For a given RF modulation type—WCDMA, for example—
the internal 150kHz fi lter provides nominal fi ltering of the
residual ripple level. Additional external fi ltering occurs in
the log domain, which introduces a systematic log error
in relation to the signal’s crest factor, as shown in the
following equation in dB.
Where CF is the crest factor and r is the duty cycle of the
measurement (or number of measurements made at the
peak envelope, divided by the total number of periodic
APPLICATIONS INFORMATION
14
Error|dB = 10 • log
Figure 12. Output Voltage Noise Density
Figure 10. RF Pulse Response Rise Time
and Fall Time vs RF Input Power
2.5
4.0
3.5
3.0
2.0
1.5
1.0
0.5
9
8
6
5
4
0
7
3
2
1
0
–30
0.1
T
T
A
A
= 25°C
= 25°C
–25
0dBm
–10dBm
–20dBm
–30dBm
NO RF INPUT
10
–20
1
INPUT POWER (dBm)
(r + (1 – r)10
FREQUENCY (kHz)
1
–15
RISE TIME
FALL TIME
10
–10
–5
100
–CF/10
0
5581 F10
5581 F12
) – CF • (r-1)
1000
5
measurements in the measurement period). It is important
to note that the CF refers to the 150kHz low pass fi ltered
envelope of the signal. The error will depend on the statistics
and bandwidth of the modulation signal in relation to the
internal 150kHz fi lter. For example, in the case of WCDMA,
simulations prove that it is possible to set the external fi lter
capacitor corner frequency at 15kHz and only introduce
an error less than 0.1dB.
Figure 11 depicts the output AM modulation ripple as a
function of modulation difference frequency for a 2-tone
input signal at 2140MHz with –10dBm input power. The
resulting deviation in the output voltage of the detector
shows the effect of the internal 150kHz fi lter.
1
Steve Murray, “Beware of Spectrum Analyzer Power Averaging Techniques,” Microwaves
& RF, Dec. 2006.
Figure 11. Output DC Voltage Deviation and Residual
Ripple vs 2-Tone Separation Frequency
Figure 13. Integrated Output Voltage Noise
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
30
25
20
15
10
0.001
5
0
0
0.1
T
T
A
A
2-TONE FREQUENCY SEPARATION (MHz)
= 25°C
= 25°C
0dBm
–10dBm
–20dBm
–30dBm
NO RF INPUT
0.01
1
FREQUENCY (kHz)
0.1
10
100
1
5581 F11
5581 F13
1000
10
0
–0.5
–1.5
–2.0
–2.5
–3.0
–1.0
5581fa