mc33411a Freescale Semiconductor, Inc, mc33411a Datasheet - Page 26

• Manufacturer Part Number: mc33411a
• Description: 900 Mhz Analog Cordless Phone Baseband With Compander
• Manufacturer: Freescale Semiconductor, Inc

Reference Oscillator/MCU Clk Out
the three PLLs, the switched capacitor filters, and the MCU
clock output. The source for the reference clock can be a
crystal in the range of 4.0 to 18.25 MHz connected to Pins
15 & 16, or it can be an external source connected to F ref In
(Pin 15). The reference frequency is directed to:
a. A programmable 12–bit counter (register bits 4/11–0) to
b. A programmable 6–bit counter (register bits 4/17–12),
c. A programmable 3–bit counter (register bits 7/16–14)
Figures 35 and 36.
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The reference oscillator provides the frequency basis for
A representation of the reference oscillator is given by
provide the reference frequency for the three PLLs. The
12–bit counter is to be set such that, in conjunction with the
programmable counters within each PLL, the proper
frequencies can be produced by each VCO.
followed by a 2 stage, to set the frequency for the switched
capacitor filters to 165 kHz, or as close to that as possible.
which provides the MCU clock output (see Tables 5 and 6).
Figure 35. Reference Oscillator Schematic
R PI
F ref In
C PI
Reference Oscillator
C 1
Gm
Xtal
C PO
F ref Out
C 2
R PO
MC33411A/B
the oscillator. Load capacitance (C L ), equivalent series
resistance (ESR), and even supply voltage will have an effect
on the oscillator response as shown in Figures 39 and 40. It
should be noted that optimum performance is achieved when
C1 equals C2 (C1/C2 = 1).
capacitance for the reference oscillator. This relationship was
defined by using a 6.0 dB minimum loop gain margin at 3.6 V.
This is considered the minimum gain margin to guarantee
oscillator start–up.
crystal load capacitance selection. In Figure 39, the
relationship between crystal load capacitance and ESR can
be seen. The lower the load capacitance the better the
performance.
can be determined from Figure 42. It should also be pointed
out that current consumption increases when C1
noise problem. An external series resistor on the crystal
output can be added to reduce the drive level, if necessary.
Input Impedance (R PI // C PI )
Output Impedance (R PO // C PO )
Figures 37 and 38 show a typical gain/phase response of
Figure 41 represents the ESR versus crystal load
Oscillator start–up is also significantly affected by the
Given the desired crystal load capacitance, C1 and C2
Be careful not to overdrive the crystal. This could cause a
Figure 36. Reference Oscillator
Input and Output Impedance
MOTOROLA RF/IF DEVICE DATA
11.6 kΩ // 2.9 pF
4.5 kΩ // 2.5 pF
C2.