SC5305A Operating & Programming Manual
Rev 2.1.0
20
Table 4. Description of the status data bits.
Bit Description
[15] 10 MHz TCXO PLL lock status
[14] 100 MHz VCXO PLL lock status
[13] LO1 PLL Main lock status
[12] LO2 PLL lock status
[11] LO3 PLL lock status
[10] LO1 PLL1 lock status
[9] LO1 PLL2 lock status
[8] Reserved
[7] External reference detected
[6] Reference output enabled
[5] Reference lock enabled
[4] IF3_FILTER1 selected
[3] RF preamplifier enabled
[2] Device standby enabled
[1] PXI 10 enable
[0] Reserved
Reading the Device Temperature
To obtain temperature data, write request register FETCH_TEMPERATURE (0x19) with 0x00 for the
instructWord, and temperature data is returned via the receivedWord pointer. Once data is received,
the least two bytes of data need to be processed to correctly represent the data in temperature units of
degrees Celsius. Data is returned in the first 14 bits [13:0]. Bit [13] is the polarity bit indicating whether it
is a positive (0x0) or negative (0x1) value. The temperature value represented in the raw data is
contained in the next 13 bits [12:0]. To obtain the temperature ADC code, the raw data should be
masked (logically ANDed) with 0x1FFF, and the polarity should be masked with 0x2000. The conversion
from 12 bit ADC code to an actual temperature reading in degrees Celsius is shown below:
Positive Temperature
=
ADC code / 32
Negative Temperature
=
(ADC code – 8192) / 32
It is not recommended to read the temperature too frequently, especially once the SC5305A has
stabilized in temperature. The temperature sensor is a serial device located inside the RF module.
Therefore, like any other serial device, reading the temperature sensor requires sending serial clock and
data commands from the processor. The process of sending clock pulses on the serial transfer line may
cause unwanted spurs on the RF signal as the serial clock potentially modulates the local oscillators.
Furthermore, once the SC5305A stabilizes in temperature, repeated readings will likely differ by as little
as 0.25
°
C over extended periods of time. Given that the gain-to-temperature coefficient is on the order
of 0.06 dB/
°
C, gain changes between readings will be negligible.
