Capacitive Load Handling - Stanford Research Systems SIM954 Operation And Service Manual

300 mhz dual inverting driver amplifier

Table of Contents

3.2 Capacitive Load Handling

SIM954 300 MHz Dual Inverting Driver Ampliﬁer

Figure 3.1: SIM954 output voltage limit as a function of load resis-

tance

Because the active part of each SIM954 ampliﬁer channel is isolated

from the load by a 3.3

the ampliﬁer's bandwidth by forming an RC-lowpass ﬁlter. The

advantage of adding an output resistor to the actual ampliﬁer is

that it will remain stable for all possible passive loads. However,

the series resistance will also limit the ampliﬁer's bandwidth when

driving capacitive loads.

A 100 pF capacitor, which is roughly equal to 1 m (3 ) of untermi-

nated RG58 coaxial cable, will form an RC-lowpass ﬁlter with 330 ps

time constant and 480 MHz corner frequency. Above the RC corner

frequency, the AC voltage on the capacitive load will fall o with an

additional 6 dB octave, but the ampliﬁer will still be able to drive up

to 1 A

AC current into the load.

peak

Capacitive loads larger than 100 pF will severely limit the bandwidth,

and in addition will also reduce the slew rate for large scale signals

because the ampliﬁer's output current is limited. The SIM954's 1 A

current limit leads to an impressive 1000 V

pacitive loads.

SIM954 Output Voltage Limit

Load Resistance [Ohm]

series resistor, capacitive loads will limit

s slew rate for 1nF ca-

3 – 3

Table of Contents

Table of Contents