MICRF506BML Micrel Inc, MICRF506BML Datasheet - Page 15

• Manufacturer Part Number: MICRF506BML
• Manufacturer: Micrel Inc

Specifications of MICRF506BML

• Operating Frequency (max): 450000kHz
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Modulation Type: FSK
• Lead Free Status / Rohs Status: Not Compliant

Frequency Synthesizer
The MICRF506 frequency synthesizer consists of a voltage-controlled oscillator (VCO), a crystal oscillator, dual
modulus prescaler, programmable frequency dividers and a phase-detector. The loop-filter is external for flexibility
and can be a simple passive circuit. The phase detector compares frequencies of two signals and produces an
error signal which is proportional to the difference between the input frequencies. The error signal is used to
control a voltage-controlled oscillator (VCO) which creates an output frequency. The output frequency is fed
through a frequency divider back to the input of the phase detector, producing a feedback loop. If the output
frequency drifts, the error signal will increase, driving the frequency in the opposite direction so as to reduce the
error. Thus the output is locked to the frequency at the other input. This input is called the reference and is
derived from a crystal oscillator, which is very stable in frequency. The block diagram below shows the basic
elements and arrangement of a PLL based frequency synthesizer. The MICRF506 has a dual modulus prescaler
for increased frequency resolution. In a dual modulus prescaler the main divider is split into two parts, the main
part N and an additional divider A, where A < N. Both dividers are clocked from the output of the dual-modulus
prescaler, but only the output of the N divider is fed into the phase detector. The prescaler will first divide by 16.
Both N and A count down until A reaches zero, at which point the prescaler is switched to a division ratio 16+1. At
this point, the divider N has completed A counts. Counting continues until N reaches zero, which is an additional
N-A counts. At this point the cycle repeats.
July 2006
0001010
0001011
0001100
0001101
0001110
0001111
0010000
0010001
0010010
0010011
A6…A0
PA
M0_7
M1_7
N0_7
N1_7
D7
-
-
-
-
-
-
Div/4
VCO
M0_6
M1_6
N0_6
N1_6
D6
-
-
-
-
-
-
1800MHz
N0_5
M0_5
N1_5
M1_5
A0_5
A1_5
D5
-
-
-
-
Prescaler
M0_4
M1_4
N0_4
N1_4
A0_4
A1_4
15
D4
-
-
-
-
XCO
M-Divider
A-Divider
N-Divider
M0_11
M1_11
N0_11
N1_11
M0_3
M1_3
N0_3
N1_3
A0_3
A1_3
D3
Loop filter
N0_10
M0_10
N1_10
M1_10
M0_2
M1_2
A0_2
N0_2
A1_2
N1_2
D2
detector
Phase
M0_9
M0_1
M1_9
M1_1
A0_1
N0_9
N0_1
A1_1
N1_9
N1_1
D1
[phone]
M9999-092904
Charge pump
N0_0
M0_8
M0_0
N1_0
M1_8
M1_0
A0_0
N0_8
A1_0
N1_8
D0