SA8025A Datasheet, PDF (13/23 Pages) NXP Semiconductors – Low-voltage 1.8GHz fractional-N synthesizer

Philips Semiconductors
1.8GHz low-voltage Fractional-N synthesizer
Product specification
SA8025A
REF_IN
L
REFERENCE
DIVIDER
“1” _D
Q
C
R
R
AUX/MAIN
DIVIDER
“1”
DR
C
X
Q
V_DDA
P
P-TYPE
CHARGE PUMP
PH
N-TYPE
CHARGE PUMP
N
V_SSA
REF_IN
L
R
X
P
N
I_PH
Figure 8. Phase Detector Structure with Timing
SR00630
Phase Detectors
The auxiliary and main phase detectors are a two D-type flip-flop
phase and frequency detector shown in Figure 8. The flip-flops are
set by the negative edges of output signals of the dividers. The
rising edge of the signal, L, will reset the flip-flops after both flip-flops
have been set. Around zero phase error this has the effect of
delaying the reset for 1 reference input cycle. This avoids
non-linearity or deadband around zero phase error. The flip-flops
drive on-chip charge pumps. A source current from the charge
pump indicates the VCO frequency will be increased; a sink current
indicates the VCO frequency will be decreased.
Current Settings
The SA8025A has 3 current setting pins: RA, RN and RF. The
active charge pump currents and the fractional compensation
currents are linearly dependent on the current connected between
the current setting pin and V_SS. The typical value R (current setting
resistor) can be calculated with the formula:
R
+
V_DDA
*
0.9 * 150
I_R
Ǹ
I_R
The current can be set to zero by connecting the corresponding pin
to V_DDA.
Auxiliary Output Charge Pumps
The auxiliary charge pumps on pin PHA are driven by the auxiliary
phase detector and the current value is determined by the external
resistor RA at pin RA. The active charge pump current is typically:
|I_PHA| + 8 @ I_RA
1996 Oct 15
13