SWR200 Просмотр технического описания (PDF) - Cirrus Logic
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SWR200 Datasheet PDF : 5 Pages
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SWR200
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3. THEORY OF OPERATION
The following refers to the schematic in Figure 1. A1 and A2 are connected as a phase-shift oscillator circuit with
the frequency set by the external capacitors C1 and C2. Q4 is included in the feedback loop of A1 as a gain control
element.
The oscillator output is fed to the chopper amplifier which develops an absolute value representation of the oscillator
output. The chopper output is compared to a precision DC reference in integrator amplifier A3. This DC error signal
is used ot control the gain setting FET Q4.
As in all precision zener based DC references, the drift of the zener becomes nonlinear at temperature extremes.
The chopper amplifier drift characteristic is complementary to this nonlinearity and compensates for the reference
drift.
4. APPLICATION INFORMATION
Figure 1 shows the connections for the SWR200 including the two frequency setting capacitors. The frequency is:
f = 10-5
C1 C2
The frequency stability is directly related to the stability of the capacitors, therefore stable capacitors like NPO ce-
ramic, or polycarbonate or polystyrene film should be used.
Two separate ground pins are provided for accurate ground sensing. This minimizes errors due to drops in the
ground pin which can become a significant source of error in sockets.
The offset of the SWR200 is fully specified for initial offset and drift and is low enough that it can normally be ne-
glected. In applications which are especially sensitive to offset the output can be AC coupled. Proper capacitor siz-
ing and high impedance sensing will minimize errors due to capacitive coupling.
EXTERNAL CONNECTIONS
PIN CONFIGURATION
TOP VIEW
C1
C1
-PS
NC
NC
NC
GND
SWR200
C2
C2
+PS
NC
NC
OUTPUT
GND SENSE
4
SWR200DS
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