ad7564ar-breel Analog Devices, Inc., ad7564ar-breel Datasheet - Page 15

• Manufacturer Part Number: ad7564ar-breel
• Description: Lc2mos +3.3 V/+5 V, Low Power, Quad 12-bit Dac
• Manufacturer: Analog Devices, Inc.

REV. A
APPLICATIONS
Programmable State Variable Filter
The AD7564 with its multiplying capability and fast settling
time is ideal for many types of signal conditioning applications.
The circuit of Figure 25 shows its use in a state variable filter
design. This type of filter has three outputs: low pass, high pass
and bandpass. The particular version shown in Figure 25 uses
the AD7564 to control the critical parameters f
stead of several fixed resistors, the circuit uses the DAC equiva-
lent resistances as circuit elements.
Thus, R1 in Figure 25 is controlled by the 12-bit digital word
loaded to DAC A of the AD7564. This is also the case with R2,
R3 and R4. The fixed resistor R5 is the feedback resistor, R
where: R
N is the DAC Digital Code in Decimal (0 < N < 4096)
DAC Equivalent Resistance, R
LADDER
V
IN
NOTES
1. A1, A2, A3, A4, : 1/4 X AD713.
2. DIGITAL INPUT CONNECTIONS ARE OMITTED.
3. C3 IS A COMPENSATION CAPACITOR TO ELIMINATE Q AND GAIN VARIATIONS
is the DAC ladder resistance
CAUSED BY AMPLIFIER GAIN AND BANDWIDTH LIMITATIONS.
V
REF
A
DAC A
(R1)
I
I
OUT1
OUT2
EQ
A
A
Figure 25. Programmable 2nd Order State Variable Filter
= (R
LADDER
I
OUT1
I
OUT2
A1
10k
DAC B
R5
B
(R2)
B
R6
O
, Q and A
R
4096)/N
FB
B
AD7564
A2
30k
R8
O
V
. In-
REF
FB
B
B.
AGND
–15–
V
REF
HIGH
PASS
OUTPUT
30k
DAC C
C3 10pF
C
(R3)
R7
In the circuit of Figure 25:
C1 = C2, R7 = R8, R3 = R4 (i.e., the same code is loaded to
each DAC).
Using the values shown in Figure 25, the Q range is 0.3 to 5 and
the f
O
range is 0 to 12 kHz.
I
I
OUT1
OUT2
C
C
Resonant Frequency, f
Quality Factor, Q = (R6/R8) (R2/R5)
A3
C1 1000pF
V
REF
Bandpass Gain, A
DAC D
D
(R4)
I
OUT2
D
I
OUT1
C2 1000pF
D
A4
O
O
= 1/(2
= –R2/R1
LOW
PASS
OUTPUT
BAND
PASS
OUTPUT
R3C1)
AD7564
3