Using The Sr446; Input - Stanford Research Systems SR446 Operation And Service Manual

1.2 Using the SR446

1.2 Using the SR446

Vin
AC/DC
50 Ω

1.2.1 Input

SR446 400 MHz Programmable Gain Preamplifier
The SR446 400 MHz Programmable Gain Preamplifier can be configured
easily by using the 7 front‑panel buttons. Settings are stored in non‑
volatile memory and restored upon power‑up.
OL
Protect
Signal
/GND
Prog.
Gain
500 Ω
Operation of the SR446 is described by the simplified block diagram
(Figure 1.3). Input coupling is either
selected by pressing the [Couple] button. AC coupling is through a
100 nF capacitor, giving a 16 kHz − 3 dB corner frequency when driven
by a 50 Ω source, AC coupled, with Term set to 50 Ω . See the ICPL
remote command (§2.3.5, pg 18).
Following the AC coupling stage, the input impedance is switched
between
50 Ω
setting can be used to provide a higher transimpedance gain for charge
and current sources—such as photomultiplier tubes—that may be
useful when the amplifier is located close to the signal source. Although
the input has protection circuitry against electrostatic discharge, users
must avoid applying continuous input signals beyond ± 4 V to avoid
damaging the amplifier front‑end components. The 50 Ω impedance
setting is intended to terminate 50 Ω coaxial cable such as RG‑58. See
the INPZ command (§2.3.5, pg 18).
The amplifier performs best when both outputs are terminated into 50 Ω
loads. Do not leave unterminated cables connected to the outputs, as
this can lead to oscillation of the amplifier. The overload indicator shows
if any output signal is over the limits or beyond the linear operating
range of the instrument. See the OVLD? query command (§2.3.9, pg 20).
Prog.
Diff.
Filter Amp
Figure 1.3: SR446 block diagram.
by pressing the [Term] button. The 500 Ω
or
500 Ω
50 Ω
× 2
50 Ω
× -2
OL Protect
, , or , and is
DC AC GND
9
+Vout
–Vout