BGT24MTR11
User's Guide
VCO Section
Application Note AN305, Rev. 1.0
2012-11-15
8 / 15
3.2
Prescalers
BGT24MTR11 has two cascaded built-in prescalers.
The first prescaler divides the oscillator’s frequency by 16,
the second reduces the output of the first one by the factor of 65536
– resulting in a total division factor of
1,048,576.
3.2.1
Divide-by-16 Prescaler
This first prescaler divides the VCO’s frequency of oscillation by the factor of 16. So at a given VCO frequency
of 24
GHz the prescaler’s output frequency is 1.5 GHz. This is a convenient frequency to feed into RF-PLLs.
The output frequency is fed differentially to pins 31 and 1 (Q1, Q1N). The differential port impedance is 100
.
Note: For proper operation of the prescaler both output pins need to be terminated by 50
. As there is DC
present at the two output pins a coupling capacitor will be necessary if the termination does not have a
DC-blocking circuit already implemented, (e.g.
a blocking capacitor at a PLL’s input).
In case a PLL does not support differential inputs it is possible to use any of the two outputs and terminate the
unused one.
Figure 5
Termination of Div16 outputs
This prescaler may be disabled by setting SPI data bit 5 (DIS_DIV16) to HIGH.
3.2.2
Divide-by-65536 Prescaler
This prescaler is fed by the divide-by-16 prescal
er’s output frequency and reduces it furtherly by the factor of
65536 resulting in a total reduction factor of 1,048,576. This means a 24 GHz VCO signal will result in an output
square wave signal of approximately 23 kHz at pin 2 (Q2).
This 23 kHz output signal c
an be monitored via a microcontroller’s timer input, for example, and then be used
together with the microcontrollers DAC or PWM output to create a
software loop to control the VCO’s output
frequency.
Note: For proper operation of this prescaler it is mandatory that the divide-by-16 prescaler is enabled. Otherwise
the divide-by-65536 will not get an input signal and will produce false output.
This prescaler may be disabled by setting SPI data bit 6 (DIS_DIV64k) to HIGH.
BGT24MTR11_Q1_connect.vsd
TEMP
Q1
VEE
Q
1
N
Q
2
V
E
E
1
2
3
30
31
32
50
Ω
50
Ω
