8-Bit Programmable Filters
818 Series
Digital Tuning &
Control Characteristics
25 Locust St, Haverhill, Massachusetts 01830 Tel: 800/252-7074, 978/374-0761 FAX: 978/521-1839
e-mail: sales@freqdev.com Web Address: http://www.freqdev.com
2
MSB
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LSB
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
0
0
0
0
0
0
0
0
f
max
/256
0
0
0
0
0
0
0
1
f
max
/128
0
0
0
0
0
0
1
1
f
max
/64
0
0
0
0
0
1
1
1
f
max
/32
0
0
0
0
1
1
1
1
f
max
/16
0
0
0
1
1
1
1
1
f
max
/8
0
0
1
1
1
1
1
1
f
max
/4
0
1
1
1
1
1
1
1
f
max
/2
1
1
1
1
1
1
1
1
fmax
Bit
Weight
fc
Corner
Frequency
+Vs
OUT
-Vs
D
D
D
D
GND
D
D
D
D
C
P
IN
Bottom View
Os/NC
4
5
3
2
1
0
6
7
Pin-Out Key
IN
OUT Analog Output Signal
GND Power and Signal Return
"P"
Transition Polarity Bit
"C"
Tuning Strobe Bit
+Vs
Supply Voltage, Positive
-Vs
Supply Voltage, Negative
Os
Optional Offset Adjustment
NC
No Connect (Highpass Models)
Analog Input Signal
D
7
Tuning Bit 7 (MSB)
D
6
Tuning Bit 6
D
5
Tuning Bit 5
D
4
Tuning Bit 4
D
3
Tuning Bit 3
D
2
Tuning Bit 2
D
1
Tuning Bit 1
D
0
Tuning Bit 0 (LSB)
Digital Tuning Characteristics
The digital tuning interface circuits are two 4042 quad CMOS
latches which accept the following CMOS-compatible inputs:
eight tuning bits (D
0
- D
7
), a latch strobe bit (C), and a transition
polarity bit (P).
Filter tuning follows the tuning equation given below:
f
c
= ( f
max
/256 ) [ 1 + D
7
x 2
2
7
+ D
6
x 2
0
]
6
+ D
5
x 2
5
+ D
4
x 2
4
+ D
3
x
3
+ D
2
x 2
2
+ D
1
x 2
1
+ D
0
x 2
where D
1
- D
7
= "0" or "1", and
f
max
= Maximum tuning frequency;
f
c
= corner frequency;
Minimum tunable frequency = f
max
/256 (D
0
thru D
7
= 0);
Minimum frequency step (Resolution) = f
max
/256
Data Control Specifications
Data Control Lines
Functions
Latch Strobe (C)
Transition Polarity (P)
Data Control Modes
Mode 1
P = 0; C = 0
frequency follows input codes
P = 0; C = 0
frequency latched on rising edge
Mode 2
P = 1; C = 1
frequency follows input codes
P = 1; C = 1
frequency latched on falling edge
Input Data Levels
Input Voltage (Vs = 15 Vdc)
Low Level In
High Level In
Input Current
High Level In
Low Level In
Input Capacitance
Latch Response
Data Set Up Time
Data Hold Time
Strobe Pulse Width
Input Data Format
Positive Logic
(CMOS Logic)
0 Vdc min.
11 Vdc min.
4 Vdc max.
15 Vdc max.
- 10
+10
5 pF typ
-5
μ
A typ.
-5
μ
A typ.
-1 mA max.
+1
μ
A max.
7.5 pF max.
1
25 nS
50 nS
80 nS min.
Frequency Select Bits
Logic "1" = +Vs
Logic "0" = Gnd
(Binary-Coded)
LSB (least significant bit)
MSB (most significant bit)
256 : 1, Binary Weighted
Bit Weighting
D
0
D
7
Frequency Range
Notes:
1.Frequency data must be present before occurrence of strobe edge.
2.Frequency data must be present after occurrence of strobe edge.