Page 5 of 15
SR446 Programmable Amplifier
Description
The SR446 is a single-channel, 400 MHz bandwidth voltage preamplifier with 21 programmable
gains from ×1 to ×100 (+0 dB to +40 dB with 2 dB steps). It also includes four programmable
low-pass filters, with settings of full bandwidth, 200 MHz, 100 MHz and 20 MHz. There are
two output channels which offer complimentary outputs (inverting and non-inverting) that can be
used separately, or together as a differential output.
The front panel displays all the setup and the state of the instrument. Users can perform all the
configurations from the front panel or remotely through the USB interface (in serial port
emulation). A connect indicator shows that a remote serial device is ready for communication.
An error indicator illuminates if any remote command errors or system errors have occurred. The
error indicator will persist for about 5 seconds. Power standby indicator shows that live AC
main is connected and ready to power up the unit.
Operation
The input impedance can be switched between 50 Ωor 500 Ω. The 500 Ω setting provides high
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. Thought input is protected, the
voltage must be limited to ±4 V to avoid damaging the amplifier front-end. The 50 Ωinput
impedance is intended to terminate 50 Ω coaxial cable such as RG-58.
The amplifier performs best when both outputs are terminated with 50 Ω. Do not leave
unterminated cables connected to the outputs, as this can cause unwanted oscillation of the
amplifier. By selecting proper output band-limiting filter, un-wanted high frequency noise can be
reduced. To protect external equipment, each output has overload detector and limiter. The
overload indicator shows if any output signal is over the limits and beyond linear operating
range.
Functional Block Diagram
Vin
-Vout
Prog.
Gain
Diff.
Amp
Prog.
Filter
DC,
AC
GND
+Vout
OL
P rote ct
OL
P rote ct
×2
×-2
50 Ω
50 Ω
50 Ω500 Ω
