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LT1206CR#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18
LT1206
7
1206fb
Typical perForMance characTerisTics
Output Impedance vs Frequency
Output Impedance in Shutdown
vs Frequency
2nd and 3rd Harmonic Distortion
vs Frequency
3rd Order Intercept vs Frequency Test Circuit for 3rd Order Intercept
FREQUENCY (Hz)
0.1
OUTPUT IMPEDANCE (Ω)
1
10
100
100k 10M 100M
1206 G19
0.01
1M
V
S
= ±15V
I
O
= 0mA
R
S/D
= 121k
R
S/D
= 0Ω
FREQUENCY (MHz)
1
–90
DISTORTION (dBc)
–80
–70
–60
–50
–30
3 10
1206 G21
–40
2 4 5 6 7 8 9
V
S
= ±15V
V
O
= 2V
P-P
2nd
3rd
R
L
= 10Ω
2nd
3rd
R
L
= 30Ω
FREQUENCY (Hz)
100
OUTPUT IMPEDANCE (Ω)
1k
10k
100k
100k 10M 100M
1206 G20
10
1M
A
V
= 1
R
F
= 1k
V
S
= ±15V
FREQUENCY (MHz)
0
10
3rd ORDER INTERCEPT (dBm)
20
30
40
50
60
5
10 15 20
1206 G22
25 30
V
S
= ±15V
R
L
= 50Ω
R
F
= 590Ω
R
G
= 64.9Ω
–
+
50Ω
LT1206
1206 TC01
65Ω
590Ω
P
O
MEASURE INTERCEPT AT P
O
LT1206
8
1206fb
siMpliFieD scheMaTic
1206 SS
V
–
OUTPUT
V
+
50Ω
D2
D1
V
–
V
+
V
+
V
–
C
C
R
C
COMP–IN+IN
SHUTDOWN
1.25k
TO ALL
CURRENT
SOURCES
Q11
Q15
Q9
Q6
Q5
Q2
Q1Q18
Q17
Q3
Q4
Q7
Q8
Q12
Q16
Q14
Q13
Q10
applicaTions inForMaTion
The LT1206 is a current feedback amplifier with high output
current drive capability. The device is stable with large
capacitive loads and can easily supply the high currents
required by capacitive loads. The amplifier will drive low
impedance loads such as cables with excellent linearity
at high frequencies.
Feedback Resistor Selection
The optimum value for the feedback resistors is a function
of the operating conditions of the device, the load imped-
ance and the desired flatness of response. The Typical AC
Performance tables give the values which result in the
highest 0.1dB and 0.5dB bandwidths for various resistive
loads and operating conditions. If this level of flatness is
not required, a higher bandwidth can be obtained by use
of a lower feedback resistor. The characteristic curves of
Bandwidth vs Supply Voltage indicate feedback resistors
for peaking up to 5dB. These curves use a solid line when
the response has less than 0.5dB of peaking and a dashed
line when the response has 0.5dB to 5dB of peaking. The
curves stop where the response has more than 5dB of
peaking.
For resistive loads, the COMP pin should be left open (see
section on capacitive loads).
Capacitive Loads
The LT1206 includes an optional compensation network
for driving capacitive loads. This network eliminates most
of the output stage peaking associated with capacitive
loads, allowing the frequency response to be flattened.
Figure 1 shows the effect of the network on a 200pF load.
Without the optional compensation, there is a 5dB peak
at 40MHz caused by the effect of the capacitance on the
output stage. Adding a 0.01µF bypass capacitor between the
output and the COMP pins connects the compensation and
completely eliminates the peaking. A lower value feedback
resistor can now be used, resulting in a response which
LT1206
9
1206fb
applicaTions inForMaTion
is flat to 0.35dB to 30MHz. The network has the greatest
effect for C
L
in the range of 0pF to 1000pF. The graph of
Maximum Capacitive Load vs Feedback Resistor can be
used to select the appropriate value of feedback resistor.
The values shown are for 0.5dB and 5dB peaking at a gain
of 2 with no resistive load. This is a worst case condition,
as the amplifier is more stable at higher gains and with
some resistive load in parallel with the capacitance. Also
shown is the – 3dB bandwidth with the suggested feedback
resistor vs the load capacitance.
Although the optional compensation works well with ca-
pacitive loads, it simply reduces the bandwidth when it is
connected with resistive loads. For instance, with a 30Ω
load, the bandwidth drops from 55MHz to 35MHz when
the compensation is connected. Hence, the compensation
was made optional. To disconnect the optional compensa-
tion, leave the COMP pin open.
Shutdown/Current Set
If the shutdown feature is not used, the SHUTDOWN pin
must be connected to ground or V
–
.
The shutdown pin can be used to either turn off the bias-
ing for the amplifier, reducing the quiescent current to
less than 200µA, or to control the quiescent current in
normal operation.
The total bias current in the LT1206 is controlled by the cur-
rent flowing out of the shutdown pin. When the shutdown
pin is open or driven to the positive supply, the part is shut
down. In the shutdown mode, the output looks like a 40pF
capacitor and the supply current is typically 100µA. The
shutdown pin is referenced to the positive supply through
an internal bias circuit (see the simplified schematic). An
easy way to force shutdown is to use open drain (collec-
tor) logic. The circuit shown in Figure 2 uses a 74C904
buffer to interface between 5V logic and the LT1206. The
switching time between the active and shutdown states
is less than 1µs.
A 24k pull-up resistor speeds up the
turn-off time and insures that the LT1206 is completely
turned off. Because the pin is referenced to the positive
supply, the logic used should have a breakdown voltage
of greater than the positive supply voltage. No other
circuitry is necessary as the internal circuit limits the
shutdown pin current to about 500µA. Figure 3 shows
the resulting waveforms.
Figure 1
Figure 2. Shutdown Interface
Figure 3. Shutdown Operation
FREQUENCY (MHz)
1
–8
VOLTAGE GAIN (dB)
–4
0
4
8
10 100
1206 F01
–6
–2
2
6
10
12
V
S
= ±15V
R
F
= 1.2k
COMPENSATION
R
F
= 2k
NO COMPENSATION
R
F
= 2k
COMPENSATION
–
+
LT1206
S/D
15V
–15V
R
F
R
G
V
IN
5V
24k
ENABLE
V
OUT
1206 F02
15V
74C906
V
OUT
ENABLE
A
V
= 1
R
F
= 825Ω
R
L
= 50Ω
R
PU
= 24k
V
IN
= 1V
P-P
1µs/DIV
1206 F03
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18

LT1206CR#TRPBF

Mfr. #:
Buy LT1206CR#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
High Speed Operational Amplifiers 250mA Out, 900V/us, 60MHz CFA
Lifecycle:
New from this manufacturer.
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