SRS Labs SR640 Series, Руководство пользователя

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17
Output Ampl i fi er
Un16A and B select the filter output or by-
passed output from the preamplifier. The
8-bit DAC U17 provides output gain ad-
j ustment. The actual output amplifier is
U119 which has its gain selected by
switch U21. Output inversion is accom-
plished with U22 in conj unction with the
switches U16C and U16D. The optional
component U23 provides a high current
output buffer. Dual Comparator U20 takes
care of output overload detection.
Optoi sol ated I nter face
No direct electrical connection exists be-
tween the microprocessor section and the
filter boards. Control signals for the fil-
ter boards originate from the two 32 bit
latched serial input shift registers U25
and U26. These shift registers are in turn
controlled by the output of optoisolator
U24. Optoisolator U11 provides output
isolation for the overload signals which
are read by the processor section. Shift
register U26 is run between -15V and
ground so that its open collector outputs
may be pulled up to +15V. These ±15V sig-
nals control the FET switches which de-
termine the filter stage frequencies.
Mi cr opr ocessor and Communi cati ons
The microprocessor U4 is a Z80, clocked
at 3.6864 MHz by U3. U6 is an 8K ROM,
while U7 provides 2K of battery backed up
RAM. U1 is a 64K ROM which contains the
calibration information for the filter
channels. The calibration ROM is mapped
as I/O, requiring flip-flop U5B to switch
between the normal I/O space and the cali-
bration ROM. U9A gates the clock to the
processor enabling the processor clock to
be removed during quiescent operation.
The clock is restored by a control signal
from flip-flop U5A in response to a key-
board or communication interrupt. Commu-
nication is accomplished with the UART
U15 and GPIB chip U12.
Power Suppl i es
Regulators U101 provides 5V power to the
microprocessor and communications cir-
cuits, while regulators U102-105 provide
±15V power to the filter sections. Note
that the 5V power supply is the only one
referenced to the chassis ground. Note
also that each filter power supply is taken
from a separate transformer secondary for
maximum isolation.
Note: The SR645 and SR650 units contain
additional regulators (U27 and U28) on the
high-pass filter boards to provide ± 5V to
the VTC4706 op-amps.
Fr ont Panel
Shift Registers U201-U206 provide control
signals for the front panel LEDs. Switches
SW301- SW324 comprise the switch matrix
which is read by the processor via input
port U 301. LED digits DS101-DS106 are
controlled via output ports U18-U25.
Ci rcui t Descri p-
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