AN-1381
APPLICATION NOTE
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How to Bypass VCO Calibration for the ADF4355-2
By Robert Brennan
7.
VCO CALIBRATION
Repeat Step 1 through Step 6 to build a lookup table for all
desired frequencies. For Step 1, writing R10, R7, R2, R1,
and R0 is only required after the first iteration. R2 and R1
are optional if they have not changed.
Bypass VCO Calibration for Faster Lock Times
For any given output frequency, the ADF4355-2 uses a certain
voltage controlled oscillator (VCO) core, band, and bias code.
These three settings are selected automatically during the VCO
automatic calibration (AUTOCAL). The settings are read from
the ADF4355-2 and stored in a lookup table. Using this lookup
table to bypass the AUTOCAL routine dramatically decreases
the total lock time when changing the frequency. For example,
lock times of less than 30 µs are possible with a 59.7 kHz loop
bandwidth. Figure 1 shows an example of a suitable loop filter.
R2
5.1kΩ
CP
C1
220pF
R1
2.4kΩ
C2
3.3nF
CORE AND BAND (R10 DB[28:26] = 1):
LE
CLK
MUXOUT
X
X
1 0 0
CORE = A
VTUNE
0
1
0 0 0
1
BAND = 70
VALUE
CORE
001
010
011
100
D
C
B
A
1
0
BIAS CODE (R10 DB[28:26] = 3):
C3
100pF
LE
fPFD = 61.44MHz
PM = 46.5°
ICP = 0.9mA
MUXOUT
X
Figure 1. Example Loop Filter with a 59.7 kHz Loop Bandwidth
VCO Readback Procedure
3.
4.
5.
6.
X
X
X
X
X
X
0
1 1
0
BIAS CODE = 6
Figure 2. VCO Readback
The VCO readback procedure is as follows:
2.
X
NOTES
1. X = DON’T CARE.
2. MUXOUT MUST BE SET TO VCO READBACK (R4, DB[29:27] = 7).
3. VCO READBACK MUST BE SET TO VCO READBACK (R7, DB[14:12] = 7).
4. DATA IS CLOCKED OUT ON THE POSITIVE EDGE OF CLK AND READ ON
THE NEGATIVE EDGE OF CLK. READBACK STARTS ON THE FIRST CLK
EDGE AFTER LE GOES HIGH. LE MUST STAY HIGH DURING A READ.
Because each ADF4355-2 chip is unique, a new lookup table
must be generated for every chip.
1.
X
13647-002
kVCO = 15MHz/V
LBW = 59.7kHz
13647-001
CLK
Load all registers to lock to the desired frequency.
a. Ensure VCO read is set to VCO core and band
(R10, DB[28:26] = 0b001) (see Figure 5).
b. Ensure VCO readback is set to VCO calibration
complete (R7, DB[14:12] = 0b110) (see Figure 4).
c. Ensure MUXOUT is set to VCO readback
(R4, DB[29:27] = 0b111) (see Figure 3).
d. Ensure AUTOCAL is enabled (R0, DB21 = 0b1); see
the ADF4355-2 data sheet for the R0 register map.
Wait until MUXOUT outputs a logic high (VCO calibration
complete).
Load R7 with VCO readback set to VCO readback (R7,
DB[14:12] = 0b111).
Pulse SPI CLK while LE is kept high. The data outputs on
MUXOUT. Extract the data as shown in Figure 2.
Load R10 with VCO read set to VCO bias code (R10,
DB[28:26] = 0b011).
Repeat Step 4 for bias data.
Bypass Automatic Calibration (AUTOCAL) to Manually
Select VCO and Lock
If the required VCO core, band, and bias code for a desired
frequency is known (for example, in a lookup table), bypass the
VCO calibration routine and set the VCO data manually with
the following steps:
1.
2.
3.
4.
5.
6.
Rev. 0 | Page 1 of 4
Load R0 with AUTOCAL disabled (R0, DB21 = 0b0). This
step is optional if AUTOCAL is already disabled.
Load R10 with VCO write set to VCO core and band (R10,
DB[31:29] = 0b001).
Load R11 with the desired VCO core, VCO band, and
VCO bias setting as defined in Figure 6. Note that the VCO
core bits are different for read and write.
Load R10 with VCO write set to VCO bias code (R10,
DB[31:29] = 0b011).
Reload R11 with the same value as in Step 3.
Lock to the desired frequency by programming R2, R1, and
R0, respectively.
AN-1381
Application Note
COUNTER
RESET
CP THREESTATE
DBR 1
PD
MUX LOGIC
CURRENT
SETTING
PD
POLARITY
DBR 1
10-BIT R COUNTER
REF MODE
DBR 1
DOUBLE BUFF
MUXOUT
RESERVED
RDIV2
REFERENCE
DOUBLER DBR 1
Expanded ADF4355-2 Register Maps
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4
0
M3
M2
M1
RD2
RD1
R10
RD2
REFERENCE
DOUBLER
0
DISABLED
1
ENABLED
R9
R8
R7
R6
R5
R4
R3
R2
R1
D1
CP4
CP3
DISABLED
0
DISABLED
ENABLED
1
DIFF
1
CP1
ICP (mA)
5.1kΩ
ENABLED
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
3.3
3.6
3.9
4.2
4.5
4.8
0
..........
0
1
1
0
..........
1
0
2
.
.
..........
.
.
.
.
.
..........
.
.
.
.
.
..........
.
.
.
1
1
..........
0
0
1020
1
1
..........
0
1
1021
1
1
..........
1
0
1022
1
1
..........
1
1
1023
M3
M2
M1
0
0
0
OUTPUT
THREE-STATE OUTPUT
0
0
1
DVDD
0
1
0
0
1
1
DGND
R DIVIDER OUTPUT
1
0
0
N DIVIDER OUTPUT
1
0
1
ANALOG LOCK DETECT
1
1
0
DIGITAL LOCK DETECT
1
1
1
VCO READBACK
C1(0)
1
CP2
0
C4(0) C3(1) C2(0)
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
U1
COUNTER
RESET
CP3
R DIVIDER (R)
U2
U1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
R1
U3
REFIN
CP4
R2
U4
SINGLE
DISABLED
..........
U5
DB0
0
0
R9
U6
DB1
U6
REFERENCE DIVIDE BY 2
R10
CP1
DB2
DOUBLE BUFFERED
REGISTER 6, BITS[DB23:DB21]
D1
RD1
1
CP2
DB3
ENABLED
U5
LDP
U2
CP
THREE-STATE
0
1.8V
0
DISABLED
1
3.3V
1
ENABLED
U4
PD POLARITY
U3
POWER DOWN
0
NEGATIVE
0
DISABLED
1
POSITIVE
1
ENABLED
13647-003
0
CONTROL
BITS
1DBR = DOUBLE BUFFERED REGISTER—BUFFERED BY THE WRITE TO REGISTER 0.
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8
0
0
1
0
0
LE
LE
0
0
0
0
0
0
0
0
0
0
VR3
VR2
VR1
0
VR3 VR2 VR1
VCO READBACK
0
0
0
0
1
1
1
1
NORMAL OPERATION
RESERVED
RESERVED
RESERVED
RESERVED
RESERVED
VCO CALIBRATION COMPLETE
VCO READBACK
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
LD5
LD4
DB7 DB6 DB5 DB4
DB3
DB2
DB1
DB0
LD2 LD1 C4(0) C3(1) C2(1) C1(1)
LOL LD3
LD1
LE SYNCHRONIZATION
CONTROL
BITS
LOCK DETECT MODE
0
FRACTIONAL-N
1
INTEGER-N (2.9ns)
LD3 LD2
FRACTIONAL-N
LD PRECISION
0
0
1
1
5.0ns
6.0ns
8.0ns
12.0ns
0
1
0
1
LOL LOSS OF LOCK MODE
0
DISABLED
0
DISABLED
1
LE SYNCED TO REFIN
1
ENABLED
Figure 4. Register 7
Rev. 0 | Page 2 of 4
LD5
LD4
LOCK DETECT CYCLE COUNT
0
0
1024
0
1
2048
1
0
4096
1
1
8192
13647-004
0
LD MODE
VCO READBACK
FRAC-N LD
PRECISION
RESERVED
LD
CYCLE
COUNT
LOL MODE
RESERVED
RESERVED
LE SYNC
Figure 3. Register 4
VCO READ
ADC
CLOCK DIVIDER
RESERVED
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8
VW2
VR3
VW1
VR2
VR1
0
1
0
0
0
0
0
0
0
0
AD8
AD7
AD6
AD5
AD4
DB7 DB6
AD3 AD2
DB5 DB4
DB3
DB2
AE1
ADC
0
DISABLED
0
0
0
0
1
1
1
1
NORMAL OPERATION
VCO CORE AND BAND
RESERVED
VCO BIAS CODE
RESERVED
RESERVED
RESERVED
RESERVED
1
ENABLED
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
VCO WRITE
NORMAL OPERATION
VCO CORE AND BAND
RESERVED
VCO BIAS CODE
RESERVED
RESERVED
RESERVED
RESERVED
AD7
..........
AD2
0
0
..........
0
1
1
0
0
..........
1
0
2
.
.
..........
.
.
.
.
.
..........
.
.
.
.
.
..........
.
.
.
1
1
..........
0
0
252
1
1
..........
0
1
253
1
1
..........
1
0
254
1
1
..........
1
1
255
AD8
DB1
DB0
AE2 AE1 C4(1) C3(0) C2(1) C1(0)
AD1
VCO READ
0
0
0
0
1
1
1
1
0
1
0
1
0
1
0
1
1
VR3 VR2 VR1
VW3 VW2 VW1
0
0
1
1
0
0
1
1
0
CONTROL
BITS
AE2
ADC CONVERSION
0
DISABLED
1
ENABLED
AD1 ADC CLK DIV
13647-005
VW3
ADC ENABLE
VCO WRITE
AN-1381
ADC
CONVERSION
Application Note
Figure 5. Register 10
VCO CORE
RESERVED
VCO BIAS
CONTROL
BITS
VCO BAND
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3
0
0
0
0
0
0
0
0
1
C4 C3 C2 C1
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
1
0
C4
C3
C2
C1
B4
B3
B2
B1
BA8
BA7 BA6 BA5 BA4 BA3 BA2
DB2
DB1
DB0
BA C4(1) C3(0) C2(1) C1(0)
VCO CORE
RESERVED
CORE D/NORMAL OPERATION
CORE C
CORE B
CORE A
B4 B3 B2 B1
VCO BIAS
BA8 BA7 .......... BA2 BA1
0
0
0
0
0
0
0
0
1
0
1
2
3/NORMAL OPERATION
4
5
6
7
8
0
0
.
.
.
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
Figure 6. Register 11
Rev. 0 | Page 3 of 4
0
0
.
.
.
1
1
1
1
..........
..........
..........
..........
..........
..........
..........
..........
..........
0
0
.
.
.
0
0
1
1
0
0
.
.
.
0
1
0
1
VCO BAND
0/NORMAL OPERATION
1
.
.
.
252
253
254
255
13647-006
0
AN-1381
Application Note
Read Timing Characteristics
Table 1. Read Timing
Parameter
t1
t2
t3
t4
t5
Limit at TMIN to TMAX
15
15
25
25
10
Unit
ns min
ns min
ns min
ns min
ns min
Description
LE high to CLK high
CLK high to DATA ready
CLK high duration
CLK low duration
CLK high to LE low (next write)
Read Timing Diagram
t1
t3
t4
CLK
t2
X
MUXOUT
DB11
DB2
DB1
DB0
t5
13647-007
LE
NOTES
1. LE MUST BE KEPT HIGH DURING READBACK.
2. X = DON’T CARE.
Figure 7. Read Timing Diagram
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registered trademarks are the property of their respective owners.
AN13647-0-11/15(0)
Rev. 0 | Page 4 of 4