AD630 Analog Devices, AD630 Datasheet - Page 4

• Manufacturer Part Number: AD630
• Description: Balanced Modulator/Demodulator
• Manufacturer: Analog Devices

20mV/DIV
20mV/DIV
TWO WAYS TO LOOK AT THE AD630
The functional block diagram of the AD630 (see page 1) also
shows the pin connections of the internal functions. An alternative
architectural diagram is shown in Figure 10. In this diagram, the
individual A and B channel preamps, the switch, and the inte-
grator output amplifier are combined in a single op amp. This
amplifier has two differential input channels, only one of which
is active at a time.
HOW THE AD630 WORKS
The basic mode of operation of the AD630 may be more easy to
recognize as two fixed gain stages which may be inserted into the
signal path under the control of a sensitive voltage comparator.
When the circuit is switched between inverting and noninverting
gain, it provides the basic modulation/demodulation function. The
AD630 is unique in that it includes Laser-Wafer-Trimmed thin-
film feedback resistors on the monolithic chip. The configuration
shown in Figure 11 yields a gain of ±2 and can be easily changed to
±1 by shifting R
The comparator selects one of the two input stages to complete
an operational feedback connection around the AD630. The
deselected input is off and has negligible effect on the operation.
AD630 –Typical Performance Characteristics
(V
(V
o
i
)
)
16
100
V
0%
90
10
i
5k
10k
14
SEL B
SEL A
20mV
20mV
15
18
20
19
10
2
9
10
19
18
B
16
20
17
1
2
9
TOP TRACE: V o
BOTTOM TRACE: V i
from its ground connection to the output.
CH
CH
A
B
2.5k
2.5k
R
A
5k
10k
15
12
13
B
A
500ns
+V
V
11
O
S
–V
8
S
R
10k
100mV/DIV
50mV/DIV
10k
F
1mV/DIV
R
TRACE
B
(V
(V
(A)
o
TOP
i
)
)
13
12
14
7
V
i
B/A
100
14
0%
90
10
30pF
1k
10k
100mV
50mV
15
TOP TRACE: V i
MIDDLE TRACE: SETTLING
ERROR (A)
BOTTOM TRACE: V o
20
TEKTRONIX
2
MIDDLE
CH A
TRACE
7A13
(A)
10k
12
1mV
When channel B is selected, the resistors R
nected for inverting feedback as shown in the inverting gain
configuration diagram in Figure 12. The amplifier has sufficient
loop gain to minimize the loading effect of R
ground produced by the feedback connection. When the sign of
the comparator input is reversed, input B will be deselected and
A will be selected. The new equivalent circuit will be the nonin-
verting gain configuration shown below. In this case R
across the op-amp input terminals, but since the amplifier drives
this difference voltage to zero the closed loop gain is unaffected.
The two closed loop gain magnitudes will be equal when R
= 1 + R
(R
The 5k and the two 10k resistors on the AD630 chip can be
used to make a gain of two as shown here. By paralleling the
10k resistors to make R
can be programmed for a gain of ± 1 (as shown in Figure 18a).
These and other configurations using the on chip resistors
present the inverting inputs with a 2.5k source impedance. The
more complete AD630 diagrams show 2.5k resistors available at
the noninverting inputs which can be conveniently used to mini-
mize errors resulting from input bias currents.
13
F
+ R
B
F
10k
10k
/R
) the parallel equivalent resistance of R
500ns
B
, which will result from making R
V
BOTTOM
TRACE
V
O
i
16
5k
10k
R
10V 20kHz
A
14
R
TRACE
1mV/DIV
F
10V/DIV
B
(V
15
TOP
(V
(B)
equal 5k and omitting R
i
)
o
V
)
i
10
20
19
18
9
2
100
0%
90
10
14
A
B
10k
10V
10V
15
TOP TRACE: V i
MIDDLE TRACE: SETTLING
ERROR (B)
BOTTOM TRACE: V o
20
HP5082-2811
2
10k
A
CH A
B
and R
13
10k
R
10k
A
1mV
at the virtual
F
12
equal to R
F
13
V
and R
B
O
±
F
the circuit
A
are con-
will appear
B
10k
.
5 s
F
R
F
/R
V
BOTTOM
TRACE
(B)
MIDDLE
TRACE
B
O
/
A