cxa3516r Sony Electronics, cxa3516r Datasheet - Page 59

• Manufacturer Part Number: cxa3516r
• Description: 3-channel 8-bit 165msps A/d Converter Amplifier Pll
• Manufacturer: Sony Electronics

The CXA3516R's charge pump is a constant-current output type as shown below.
The PLL closed loop transmittance is obtained by the following formula.
Here, KPD, F(S) and KVCO are:
1
KPD:
F(S):
KVCO: VCO gain (rad/s/V)
Performing Laplace conversion:
o (t)/N =
o (t = 0) = 0
o (t)/N =
o (S)/N =
The reason for the 1/S inside the phase detector is as follows.
o/N
V
r
CC
Phase comparator gain (A/rad)
Loop filter transmittance ( )
=
o
o
t
t
1
s
S2
r
S1
W
1 + KPD · F (S) · KVCO · 1/N · 1/S
0
0
(t)/Ndt + o (t = 0)/N: (a)
KPD · F (S) · KVCO · 1/N · 1/S
(t)/Ndt: (b)
0
1/S
(S)/N: (c)
To LPF
+
r
–
1/S
When a constant-current output charge pump circuit is used inside the PLL,
the phase detector (PD) output acts as a current source, and the dimension of
its transmittance KPD is A/rad. Also, when considering the VCO input as a
voltage, the LPF transmittance dimension must be expressed in ohms (
V/A).
Therefore, the PLL transmittance when a constant-current output charge
pump circuit is used is as follows.
N
o
0
(A/rad)
/N
KPD
PD
counter
1/N
– 59 –
... (1)
F (S)
LPF
( )
(rad/S/V)
KVCO
VCO
0
CXA3516R
=