Rev. 1.0, 02/00, page 555 of 1141
Section 26 Servo Circuits
26.1
Overview
26.1.1
Functions
Servo circuits for a video cassette recorder are included on-chip.
The functions of the servo circuits can be divided into four groups, as listed in table 26.1.
Table 26.1
Servo Circuit Functions
Group
Function
Description
CTL I/O amplifier
Gain variable input amplifier
Output amplifier with rewrite mode
CFGDuty compensation
input
Duty accuracy: 50
±
2%
(Zero cross type comparator)
DFG, DPG
separation/overlap input
Overlap input available: Three-level input method, DFG
noise mask function
Reference signal
generators
V compensation, field detection, external signal sync, V
sync in REC mode, REF30 signal output to outside
HSW timing generator
Head-switching signals, FIFO 20 stages
Compatible with DFG counter soft-reset
Four-head high-speed
switching circuit for special
playback
Chroma-rotary/head-amplifier switching output
12-bit PWM
Improved speed of carrier frequency
Frequency division circuit
With CFG mask, no CFG for phase or CTL mask
(1) Input and output
circuits
Sync detection circuit
Noise count, field discrimination, Hsync compensation,
Hsync detection noise mask
Drum speed error detector
Lock detector function, pause at the counter overflow,
R/W error latch register, limiter function
Drum phase error detector
Latch signal selectable, R/W error latch register
Capstan speed error
detector
Lock detector function, pause at the counter overflow,
R/W error latch register, limiter function
Capstan phase error
detector
R/W error latch register
(2) Error detectors
X-value adjustment and
tracking adjustment circuit
(Separate setting available)
(3) Phase and gain
compensation
Digital filter computation
circuit
Computations performed automatically by hardware
Output gain variable:
×
2 to
×
64 (exponents of 2)
(Partial write in Z
-1
(high-order 8 bits) available)
Additional V signal circuit
Valid in special playback
(4) Other circuits
CTL circuit
Duty discrimination circuit, CTL head R/W control,
compatible with wide aspect