Datasheet
LTC1099
11
ANALOG INTERFACE
UU
APPLICATIONS
Analog Multiplier
The schematic Figure 9 shows the LTC1099 configured
with a DAC to form a two quadrant analog multiplier. An
input waveform is applied to the LTC1099 where it is
digitized at a 300kHz rate. The digitized signal is fed to the
DAC in “flow-through” mode where another signal is input
to the DAC reference input. In this way, the two analog
signals are multiplied to produce a double sideband ampli-
tude modulated output. Figure 10 shows a 3kHz sine wave
multiplied by a 100Hz triangle.
–
+
1
2
3
4
5
6
7
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
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7
8
9
10
11
12
14
13
12
11
10
9
8
20
19
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12
11
24
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13
N/C
N/C
N/C
CLK
3MHz
OSC
5V
5V
OUT
74LS90
LT1019-5
÷ 10 = 300kHz
= ANALOG GROUND
= DIGITAL GROUND
15V
IN
5V
REF
AGND
25k
OUT
TRIM
GND
IN
LTC1099
DB0
DB1
DB2
DB3
WR/RDY
MODE
RD
INT
GND
CS
WR1
GND
DI5
DI4
DI3
DI2
DI1
DI0
V
REF
RFB
V
CC
WR2
XFER
DI6
DI7
DI8
DI9
DI10
DI11
I
OUT2
I
OUT1
DB7
DB6
DB5
DB4
CS
REF
+
REF
–
BYTE 1/
BYTE 2
(V
IN1
) 0V TO 5V
ANALOG
INPUT
(V
IN2
) +10V TO –10V
ANALOG
INPUT
CS AND RD LOW
4
DB0-DB3
4
DB4-DB7
88
MICROLINEAR
MP1208 DAC
12V
10µF
4.7µF
0.01µF
10µF
50k
OFFSET NULL
15V
–15V
15V
10pF
1
5
LT1056
5V
Figure 9
Note that since this is only a two quadrant multiplier, a
carrier component (the input to the LTC1099) will appear
in the output spectrum. Figure 11 shows the frequency
spectrum of a 42.5kHz sine wave multiplied by a 5kHz sine
wave. The depth of modulation is about 30dB. Figure 12
shows a 42.375kHz sine wave multiplied by a 30.875kHz
sine wave. Note that at these higher frequencies, the depth
of modulation is still about 30dB. The carrier feed-through
is seen in Figure 12.
V
IN1
≅ 0V TO 5V
TRIANGLE INTO LTC1099
~100Hz
V
IN2
≅ ±4.8V SINE
INTO DAC ~ 3kHz
1099 F10
Figure 10