SA8025A データシートの表示（PDF） - Philips Electronics
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SA8025A Datasheet PDF : 23 Pages
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Philips Semiconductors
1.8GHz low-voltage Fractional-N synthesizer
Product specification
SA8025A
REFERENCE R
MAIN N
VCO CYCLES
DETECTOR
OUTPUT
CONTENTS
ACCUM.
FRACTIONAL
COMPENSATION
CURRENT
N
N
2
N+1
N
N+1
4
1
3
0
TIME
PULSE-WIDTH
MODULATION
mA
OUTPUT ON
PHP, PHI
µA
PULSE-LEVEL
MODULATION
Figure 9. Waveforms for NF = 2, Fraction = 0.4
Main Output Charge Pumps and Fractional
Compensation Currents
The main charge pumps on pin PHP and PHI are driven by the main
phase detector and the current value is determined by the current at
pin RN and via a number of DACs which are driven by registers of
the serial input. The fractional compensation current is determined
by the current at pin RF, the contents of the fractional accumulator
FRD and a number of DACs driven by registers from the serial input.
The timing for the fractional compensation is derived from the
reference divider. The current is on during 1 input reference cycle
before and 1 cycle after the output signal to the phase comparator.
Figure 9 shows the waveforms for a typical case.
When the serial input A word is loaded, the output circuits are in the
“speed-up mode” as long as the STROBE is H, else the “normal
mode” is active. In the “normal mode” the current output PHP is:
IPHP_N + IPHP ) IPHP_comp
where:
|IPHP|
+
CN @ IRN
32
:charge pump current
|IPHP_comp|
+
FRD
@
IRF
128
:fractional comp.
current
The current in PHI is zero in “normal mode”.
In “speed-up mode” the current in output PHP is:
IPHP_S + IPHP ) IPHP_comp
ǒ Ǔ |IPHP| +
CN @ IRN
32
(2CL)1 ) 1)
ǒ Ǔ |IPHP_comp| +
FRD @ IRF
128
(2CL)1 ) 1)
In “speed-up mode” the current in output PHI is:
IPHI_S + IPHI ) IPHI_comp
where:
ǒ Ǔ |IPHI| +
CN @ IRN
32
(2CL)1) CK
1996 Oct 15
14
SR00560
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