SP8400
Very Low Phase Noise Synthesiser Divider
The SP8400 is a very low phase noise programmable
divider which is based on a divide by 8/9 dual modulus
prescaler and a 12 stage control counter. This gives a minimum
division ratio of 56 (64 for fractional - N synthesis applications),
and a maximum division ratio of 4103. Special circuit
techniques have been used to reduce the phase noise
considerably below that produced by standard dividers.The
data inputs are CMOS or TTL compatible.
The SP8400 is packaged in a 28 pin plastic SO package.
FEATURES
s
Very low Phase Noise (Typically -156dBc/Hz at 1kHz
offset)
s
Supply Voltage 5V
ABSOLUTE MAXIMUM RATINGS
Supply Voltage
6.5V
Output Current
20mA
Storage Temperature Range
-55
C to +125
C
Maximum Clock Input Voltage
2.5V p-p
ORDERING INFORMATION
SP8400 KG MPES(Commercial Grade)
MP28
Fig.1 Pin connections - top view
DS3739 - 2.1 April 1994
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
M2
M1
M0
V
CC
+5V
GND
CLOCK INPUT
CLOCK INPUT
CLOCK INPUT
GND
V
CC
+5V
V
CC
+5V
GND
A0
M3
M4
M5
M6
M7
M8
N/C
OUTPUT
OUTPUT
N/C
V
CC
+5V
N/C
A2
A1
CLOCK INPUT
Fig.2 Typical single sideband phase noise measured at 300MHz
(f) (dBc/Hz) 3dB
Frequency (Hz)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
10
100
1k
10k
100k
2
SP8400
Fig.3 Typical input sensitivity
ELECTRICAL CHARACTERISTICS
Guaranteed over: Supply voltage V
CC
= +4.75V to +5.25V Temperature T
amb
= -10
C to +75
C
Tested at +4.75V and +5.25V at T
amb
= +25
C
FREQUENCY MHz
400
300
200
100
0
200
400
600
800
1000
1200
1400
355mV
140mV
1600
500
600
OPERATING WINDOW
V
in
mV rms
Min.
Typ.
Max.
Supply current
Output voltage swing
Input sensitivity 200MHz to 1.5GHz
Data Inputs
Logic high voltage
Low low voltage
Input current
137
410
152
140
(-4)
0.8
180
122
320
2.2
4, 11, 12, 18
20, 21
7, 8
Output loaded with 300R See Fig.4
p-p @ 1.5GHz input
71 mode
See Fig.4
RMS Sine wave into 50 Ohms
(dBm equivalent) See Fig.3
5V Data input voltage
mA
mV
mV
dBm
V
V
A
Units
Value
Conditions
Characteristic
Pin
3
SP8400
APPLICATIONS INFORMATION
Circuit description, synthesiser divider
The divider is based on a divide by 8/9 modulus prescaler,
and a 12 stage control counter. This gives minimum fractional
N division ratio of 64 (56 for general division), and a maximum
division ratio of 4103. The inputs to the control counter are TTL/
CMOS compatible. There is a fixed offset of 8 between the
number on the data lines and the actual division ratio.
The output is one transition only per divide cycle. This
eliminates the problem of where to put the redundant edge
when the divider is used in a fractionalN system, and also
avoids the problem of how to define the output pulse width. This
means that the overall division ratio conventionally defined in
terms of the rate of edges of the same polarity is twice the
selected division ratio.
Fig.4 Test circuit
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
SP8400
10nF
10nF
1nF
1nF
2x330R
1nF
RF
TTL/CMOS
MODULUS
CONTROL
TTL/CMOS
MODULUS
CONTROL
V
CC
50R
50R
SIGNAL
GENERATOR
220nF
OUTPUT
Equations for division
The M and A data inputs form a 12 bit number with A0
being the least significant bit and M8 being the most significant
bit.
Definition 1:
Division ratio (input frequency to output
edges, positive or negative).
= Number loaded + 8
Definition 2:
Division ratio (input frequency to output
frequency).
= (Number loaded + 8) x 2
4
SP8400
Fig.5 Typical application combining output to increase signal and retain low phase noise
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
SP8400
10nF
10nF
1nF
1nF
2x330R
1nF
M
+5V
50R
CLOCK INPUT
INPUTS
A
INPUTS
10nF
330R
1k
+15V
2 x BF569
(or similar)
Available division ratio
All division ratios of 64 to 4103 (Definition 1) will return the
divider to the same internal state at the end of the count and
hence these are the only divisional ratios to be used for
fractionalN synthesiser application.
All division ratios of 56 to 4103 are available for general division
purposes. Additional division ratios available for general
division are:-
8,9
16, 17, 18
24, 25, 26, 27
32, 33, 34, 35, 36
40, 41, 42, 43, 44, 45
48, 49, 50, 51, 52, 53, 54
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