LTC1757A-1EMS8 Linear Technology, LTC1757A-1EMS8 Datasheet - Page 11

• Manufacturer Part Number: LTC1757A-1EMS8
• Description: IC CTRLR RF POWER SINGLE 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC1757A-1EMS8

• Rf Type: Cellular, GSM, PCS, Wireless Modem, TDMA
• Frequency: 850MHz ~ 2GHz
• Features: Single Output
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

External pole frequencies within the loop may further
reduce phase margin. The phase margin degradation, due
to external and internal pole combinations, is difficult to
determine since complex poles are present. Gain peaking
may occur, resulting in higher bandwidth and lower phase
margin than predicted from the open loop Bode plot. A low
frequency AC SPICE model of the LTC1757A power
APPLICATIO S I FOR ATIO
Figure 6. SPICE Model Open Loop Gain and Phase
Characteristics from RF to V
Figure 4. Measured Open Loop Gain and Phase
–20
–40
–20
–30
–40
–50
–60
–10
80
60
40
20
80
70
60
50
40
30
20
10
0
0
100
100
1k
1k
U
FREQUENCY (Hz)
FREQUENCY (Hz)
10k
GAIN
10k
U
GAIN
PHASE
PHASE
100k
100k
PCA
C
R
R
C
LOAD
LOAD
LOAD
LOAD
W
1M
1M
= 33pF
= 2k
= 33pF
= 2k
1757A F04
1757A F06
10M
10M
200
150
100
50
0
–50
–100
180
160
140
120
100
80
60
40
20
0
–20
–40
–60
–80
–100
U
controller is included to better determine pole and zero
interactions. The user can apply external gains and poles
to determine bandwidth and phase margin. DC, transient
and RF information cannot be extracted from the present
model. The model is suitable for external gain evaluations
up to 6 . The 1.25MHz PCTL input filter limits the band-
width, therefore, the RF input is used in the model.
PCTL
Figure 7. SPICE Model Closed Loop Voltage Gain
–10
–20
–25
–15
LTC1757A-1/LTC1757A-2
–5
+
5
0
I
FB
100
EXTERNAL GAIN = 3
C
R
Figure 5. Closed Loop Block Diagram
LOAD
LOAD
–
BW1 400kHz
RF DETECTOR
BANDWIDTH = 1.35MHz
AMPLIFER
LTC1757A
= 33pF
CONTROL
= 2k
1k
G1
H1
FREQUENCY (Hz)
10k
V
RF
PCA/B
14dB to 20dB LOSS
RF POWER AMP
100k
DIRECTIONAL
COUPLER
G2
H2
1M
1757A F05
1757A F07
10M
CONTROLLED
RF OUTPUT
POWER
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