ADF5901 Data Sheet
Rev. A | Page 24 of 26
5. Write 0x809FE560 to Register R0 to power Tx1 on, Tx2 off,
and LO on.
6. Write 0x809FED60 to Register R0 to set the Tx1 amplitude
calibration (400 µs).
7. Write 0x89FE5A0 to Register R0 to power Tx1 off, Tx2 on,
and LO on.
8. Write 0x809FF5A0 to Register R0 to set the Tx2 amplitude
calibration (400 µs).
9. Write 0x2800B929 to Register R9.
10. Write 0x809F25A0 to Register R0 to disable the R and N
counters.
TEMPERATURE SENSOR
The ADF5901 has an on-chip temperature sensor that can be
accessed on the ATEST pin or as a digital word on DOUT
following an ADC conversion. The temperature sensor operates
over the full operating temperature range of −40°C to +105°C.
The accuracy can be improved by performing a one-point
calibration at room temperature and storing the result in
memory.
With the temperature sensor on the analog test bus and test bus
connected to the ATEST pin (Register 4 set to 0x0000A064) the
ATEST voltage can be converted to temperature with the
following equation:
( )
GAIN
OFF
ATEST
V
VV
eTemperatur
−
=
C)(
(3)
where:
V
ATEST
is the voltage on the ATEST pin.
V
OFF
= 0.699 V, the offset voltage.
V
GAIN
= 6.4 × 10
−3
, the voltage gain.
The temperature sensor result can be converted to a digital
word with the ADC and readback on DOUT with the following
sequence:
1. Write 0x809FA5A0 to Register R0 to enable the counters.
2. Write 0x00012064 to Register R4 to connect the analog test
bus to the ADC and V
TEMP
to the analog test bus.
3. Write 0x00028C82 to Register R2 to start the ADC
conversion.
4. Write 0x018902C3 to Register R3 to set the output ADC
data to DOUT.
5. Read back DOUT.
6. Write 0x809F25A0 to Register R0 to disable R and N
counters.
Convert the DOUT word to temperature with the following
equation:
( )( )
GAIN
OFFLSB
V
VVADC
eTemperatur
−×
=C)(
(4)
where:
ADC is the ADC code read back on DOUT.
V
LSB
= 7.33 mV, the ADC LSB voltage.
V
OFF
= 0.699 V, the offset voltage.
V
GAIN
= 6.4 × 10
−3
, the voltage gain.
RF SYNTHESIS: A WORKED EXAMPLE
The following equation governs how to program the ADF5901:
RF
OUT
= (INT + (FRAC/2
25
)) × (f
REF
) × 2 (5)
where:
RF
OUT
is the RF frequency output.
INT is the integer division factor.
FRAC is the fractionality.
f
REF
= REF
IN
× ((1 + D)/(R × (1 + T))) (6)
where:
REF
IN
is the reference frequency input.
D is the reference doubler bit, DB10 in Register R7 (0 or 1).
R is the reference division factor.
T is the reference divide by 2 bit, DB11 in Register R7 (0 or 1).
For example, in a system where a 24.125 GHz RF frequency
output (RF
OUT
) is required and a 100 MHz reference frequency
input (REF
IN
) is available, f
REF
is set to 50 MHz.
From Equation 6,
f
REF
= (100 MHz × (1 + 0)/(1 × (1 + 1)) = 50 MHz
From Equation 5,
24.125 GHz = 50 MHz × (N + FRAC/2
25
) × 2
Calculating the N and FRAC values,
N = int(RF
OUT
/(f
REF
× 2)) = 241
FRAC = F
MSB
× 2
13
+ F
LSB
F
MSB
= int(((RF
OUT
/(f
REF
× 2)) − N) × 2
12
) = 1024
F
LSB
= int(((((RF
OUT
/(f
REF
× 2)) − N) × 2
12
) − F
MSB
) × 2
13
) = 0
where:
F
MSB
is the 12-bit MSB FRAC value in Register R5.
F
LSB
is the 13-bit LSB FRAC value in Register R6.
int() makes an integer of the argument in parentheses.
