858 Series
8-Bit Programmable Filters
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 + D
6
x 2 + D
5
x 2 + D
4
x 2 + D
3
x
2 + D
2
x 2 + D
1
x 2 + 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
3
2
1
0
7
6
5
4
Digital Tuning &
Control Characteristics
Pin-Out Key
IN
OUT
GND
“P”
“C”
+Vs
-Vs
Os
Analog Input Signal
Analog Output Signal
Power and Signal Return
Transition Polarity Bit
Tuning Strobe Bit
Supply Voltage, Positive
Supply Voltage, Negative
Offset Adjustment
D
7
Tuning
D
6
Tuning
D
5
Tuning
D
4
Tuning
D
3
Tuning
D
2
Tuning
D
1
Tuning
D
0
Tuning
Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
7 (MSB)
6
5
4
3
2
1
0 (LSB)
OUT +Vs -Vs
D
7
D
6
D
5
D
4
GND
D
3
D
2
D
1
D
0
IN Os
Data Input Specifications
Data Control Lines
Functions
Latch Strobe (C)
Transition Polarity (P)
frequency follows input codes
frequency latched on rising edge
frequency follows input codes
frequency latched on falling edge
Data Control Modes
Mode 1
P = 0; C = 0
P = 0; C = 0›
Mode 2
P = 1; C = 1
P = 1; C = 1fl
Bottom View
P C
MSB
Input Data Levels
(CMOS Logic)
4 Vdc max.
15 Vdc max.
-1
mA
max.
.
+1
mA
max.
7.5 pF max.
0
0
0
0
0
1
2
7
---
2
6
---
2
5
---
2
4
---
2
3
---
2
2
---
2
1
LSB
2
0
Bit
Weight
Corner
Frequency
fc
Input Voltage (Vs = 15 Vdc)
Low Level In
0 Vdc min.
High Level In
11 Vdc min.
Input Current
High Level In
Low Level In
Input Capacitance
Input Data Format
Positive Logic
Bit Weighting
D
0
D
7
Frequency Range
- 10
mA
typ.
-5
+10
mA
typ
.
5 pF typ
-5
D
7
0
0
0
D
6
0
0
0
0
0
0
0
1
1
D
5
0
0
0
0
0
0
1
1
1
D
4
0
0
0
0
0
1
1
1
1
D
3
0
0
0
0
1
1
1
1
1
D
2
0
0
0
1
1
1
1
1
1
D
1
0
0
1
1
1
1
1
1
1
D
0
0
1
1
1
1
1
1
1
1
f
max
/256
f
max
/128
f
max
/64
f
max
/32
f
max
/16
f
max
/8
f
max
/4
f
max
/2
fmax
Frequency Select Bits
Logic "1" = +Vs
Logic "0" = Gnd
(Binary-Coded)
LSB (least significant bit)
MSB (most significant bit)
256 : 1, Binary Weighted
Notes:
1. Frequency data must be present before occurrence of strobe edge.
2. Frequency data must be present after occurrence of strobe edge.
2
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