mc12040p Lansdale Semiconductor, Inc., mc12040p Datasheet - Page 4

• Manufacturer Part Number: mc12040p
• Description: Phase?frequency Detector
• Manufacturer: Lansdale Semiconductor, Inc.

ML12040
Legacy Applications Information
comparator for MECL–compatible input signals. It determines
the “lead” or “lag” phase relationship and the time difference
between the leading edges of the waveforms. Since these edges
occur only once per cycle, the detector has a range of ±2π radians.
waveforms, R and V (Figure 2), of the same frequency but dif-
fering in phase. If the logic had established by past history that
R was leading V, the U output of the detector (pin 4) would
produce a positive pulse width equal to the phase difference
and the D output (Pin 11 ) would simply remain low.
(Figure 2), giving rise to a positive pulse on the D output and a
constant low level on the U output pin. Both outputs for the
sample condition are valid since the determination of lead or
lag is dependent on past edge crossing and initial conditions at
start–up. A stable phase–locked loop will result from either
condition.
that is, the ratio of the output pulse width to total period. By inte-
grating or low–pass filtering the outputs of the detector and shift-
ing the level to accommodate ECL swings, usable analog infor-
mation for the voltage controlled oscillator can be developed. A
circuit useful for this function is shown in Figure 3.
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The ML12040 is a logic network designed for use as a phase
Operation of the device may be illustrated by assuming two
On the other hand, it is also possible that V was leading R
Phase error information is contained in the output duty cycle
(D Output = “0”)
(D Output = “0”)
R Leads V
V Leads R
R
V
Figure 2. Timing Diagram
Lead
Lag
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ML12040
the operational amplifier from the normally high outputs of the
phase detector (U and D). Using this technique the quiescent
differential voltage to the operational amplifier is zero (assum-
ing matched “1” levels from the phase detector). The U and D
outputs are then used to pass along phase information to the
operational amplifier. Phase error summing is accomplished
through resistors R1 connected to the inputs of the operational
amplifier. Some R–C filtering imbedded within the input net-
work (Figure 3) may be very beneficial since the very narrow
correctional pulses of the ML12040 would not normally be
integrated by the amplifier. Phase detector gain for this config-
uration is approximately 0.16 volts/radian.
operational amplifier, mismatching of nominally equal resis-
tors, and mismatching of phase detector “high” states between
the outputs used for threshold setting and phase measuring. All
these effects are reflected in the gain constant. For example, a
16 mV offset voltage in the amplifier would cause an error of
0.016/0.16 = 0.1 radian or 5.7 degrees of error. Phase error can
be trimmed to zero initially by trimming either input offset or
one of the threshold resistors (R1 in Figure 3). Phase error
over temperature depends on how much the offending parame-
ters drift.
Proper level shifting is accomplished by differentially driving
System phase error stems from input offset voltage in the
Figure 3. Typical Filter and Summing Network
U
D
12
3
510
510
R1
R1
2
2
C C
C C
R1
R1
2
2
R 2
C
LANSDALE Semiconductor, Inc.
R 2
–
+
MC1741
10 to
30V
C
To
VCO
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