Datasheet

LT6600-10
10
66001fe
APPLICATIONS INFORMATION
Figure 5, present the output of the LT6600-10 with a 1600
differential load, or the equivalent of 800 to ground at
each output. The impedance seen by the network analyzer
input is still 50, reducing refl ections in the cabling be-
tween the transformer and analyzer input.
voltage of V
MID
. While the internal 11k resistors are well
matched, their absolute value can vary by ±20%. This
should be taken into consideration when connecting an
external resistor network to alter the voltage of V
MID
.
Figure 5. (S8 Pin Numbers)
–
+
0.1µF
0.1µF
2.5V
–2.5V
–
+
LT6600-10
3
4
1
7
2
8
5
6
6600 F05
402
402
NETWORK
ANALYZER
INPUT
50
COILCRAFT
TTWB-16A
4:1
NETWORK
ANALYZER
SOURCE
COILCRAFT
TTWB-1010
1:1
50
53.6
388
388
Figure 6
1MHz INPUT LEVEL (V
P-P
)
0
20
0
–20
–40
–60
–80
–100
–120
35
6600 F06
12
46
OUTPUT LEVEL (dBV)
3RD HARMONIC
85°C
1dB PASSBAND GAIN
COMPRESSION POINTS
1MHz 25°C
1MHz 85°C
3RD HARMONIC
25°C
2ND HARMONIC
25°C
2ND HARMONIC
85°C
Differential and Common Mode Voltage Ranges
The differential amplifi ers inside the LT6600-10 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the fi lter. This limiting function prevents
excessive power dissipation in the internal circuitry
and provides output short-circuit protection. The limiting
function begins to take effect at output signal levels above
2V
P-P
and it becomes noticeable above 3.5V
P-P
. This is
illustrated in Figure 6; the LTC6600-10 was confi gured with
unity passband gain and the input of the fi lter was driven
with a 1MHz signal. Because this voltage limiting takes
place well before the output stage of the fi lter reaches the
supply rails, the input/output behavior of the IC shown
in Figure 6 is relatively independent of the power supply
voltage.
The two amplifi ers inside the LT6600-10 have independent
control of their output common mode voltage (see the
Block Diagram section). The following guidelines will
optimize the performance of the fi lter for single-supply
operation.
V
MID
must be bypassed to an AC ground with a 0.01µF or
higher capacitor. V
MID
can be driven from a low impedance
source, provided it remains at least 1.5V above V
–
and at
least 1.5V below V
+
. An internal resistor divider sets the
V
OCM
can be shorted to V
MID
for simplicity. If a different
common mode output voltage is required, connect V
OCM
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at V
OCM
must be less than or equal to
the mid-supply level. For example, voltage (V
OCM
) ≤1.65V
on a single 3.3V supply. For power supply voltages higher
than 3.3V the voltage at V
OCM
can be set above mid-supply.
The voltage on V
OCM
should not be more than 1V below
the voltage on V
MID
. The voltage on V
OCM
should not be
more than 2V above the voltage on V
MID
. V
OCM
is a high
impedance input.
The LT6600-10 was designed to process a variety of input
signals including signals centered around the mid-supply
voltage and signals that swing between ground and a
positive voltage in a single-supply system (Figure 1).
The range of allowable input common mode voltage (the
average of V
IN
+
and V
IN
–
in Figure 1) is determined by
the power supply level and gain setting (see the Electrical
Characteristics section).
Common Mode DC Currents
In applications like Figure 1 and Figure 3 where the
LT6600-10 not only provides lowpass fi ltering but also level
shifts the common mode voltage of the input signal, DC