background image

 
The  1kΩ  resistors  will  form  a  voltage 
divider  with  the  output  resistance  of  the 
signal  source  which  is  used  to  drive  the 
WMA-200  amplifier.  If  this  impedance  is 
very  low,  no  change  in  gain  will  be 
observable,  but  if  this  source  has  e.g.  a 
(commonly  encountered)  50Ω  output 
resistance,  the  apparent  gain  will  change 
from  20x  to  a  lower  but  very  well-defined 
19.05x due to this voltage divider effect.  
 
The  1kΩ  resistors  also  add  to  the  output 
offset voltage because the offset current of 
the  input  amplifier  generates  a  voltage 
over  these  resistors.  This  output  offset 
voltage  is  ~3mV  if  the  BNC  input  is  used 
with  a  50Ω  signal  generator.  When  both 
inputs  are  shorted  together  or  connected 
to  a  low-impedance  source,  the  offset  is 
reduced to ~700 μV. 

 
Using the BNC connector, the amplifier will 
amplify  20.0x,  up  to  the  maximum  output 
voltage.  To  obtain  the  lowest  possible 
noise performance possible, it is highly  
 
recommended  to  use  the  differential  input 
instead  of  the  BNC.  The  BNC  input  is 
internally connected to the positive input of 
the  differential  connector  (see  Fig.  1  for 
the connections). The negative input of the 
differential  connector  should  be  supplied 
with the same input signal as the positive 
input,  but  this  signal  should  have  the 
opposite  polarity.  Both  of  the  differential 
inputs amplify 20.0x, which means that the 
absolute  amplitude  of  either  input  should 
be  only  half  of  the  value  that  would  be 
used to drive the BNC input.  
 

 

 

 

Figure 1. Signals to be supplied to the BNC and differential connector 

 
A  low  noise  amplifier  like  the  WMA-200 
model can never be made fully insensitive 
to input overload conditions, as this would 
limit  the  performance  of  the  amplifier 
significantly.  For  normal  operation,  input 
voltages  should  remain  in  the  –8.75V  to 
+8.75V  range  when  using  the  BNC  input, 
and  half  this  value  when  using  the 
differential connector. This will result, with 
an  amplification  of  20.0x,  in  an  output 
voltage swing of –175V to +175V. Below -
15V and above +15V, the input protection 
circuitry  will  limit  the  voltage  fed  to  the 
amplifier,  but  the  amplifier  (or  the  signal 
source)  may  be  permanently  damaged  if 
the current of the source is not limited.  
 

 

Outputs  

 
The  WMA-200  model  has  a  50Ω  output 
resistance,  and  has  been  designed  to  be 

fully stable with all capacitive loads. It has 
been  optimized  for  a  perfect  step-
response, but it is also a very good linear 
and sine-wave amplifier. 
The  WMA-200  amplifier  has  a  clever 
feedback  system,  which  ensures  that  no 
significant  overshoot  occurs  at  any 
capacitive  load.  The  bandwidth  of  the 
amplifier  is  automatically  reduced  to 
ensure stability. Instability under capacitive 
loading conditions is a common problem of 
other  high-speed  negative  feedback 
amplifiers,  often  resulting  in  unwanted 
output overshoot voltages, and, in extreme 
cases, oscillations. 
Short-circuiting this amplifier will not break 
down  the  amplifier,  due  to  the  extremely 
fast  current  limiting  circuit  that  has  been 
employed.  
 
The  output  impedance  of  the  WMA-200 
model  is  50Ω,  to  ensure  stability  with  all 

Inverting (-)

Non-inverting (+)

Ground

Содержание WMA-200

Страница 1: ...ifier getting started The Falco Systems WMA 200 model is a high quality high voltage linear laboratory amplifier optimized for experiments requiring world class ultra low output noise The excellent no...

Страница 2: ...afety This product is able to produce over 175V at more than 150mA at its output which is a very high level risk of electric shock Safety measures should be taken accordingly This is indicated by the...

Страница 3: ...he BNC input Figure 1 Signals to be supplied to the BNC and differential connector A low noise amplifier like the WMA 200 model can never be made fully insensitive to input overload conditions as this...

Страница 4: ...tions an effect related to the finite speed of light and current limiting due to the cable capacitance Although the amplifier itself remains fully stable using less than 3 meter of input and output ca...

Страница 5: ...tive load box accessory can be ordered from Falco Systems for use with the amplifier which is connected in parallel with the load Fig 4 This will bring the noise down from its value of 50 Vrms with a...

Страница 6: ...utput noise voltage versus capacitive load Fig 7 Noise and offset with and without capacitive load box Fig 8 Sine and triangle wave responses Fig 10 11 Square wave response Fig 12 13 14 Step response...

Страница 7: ...nnected The corresponding signal bandwidths of the amplifier are DC 100kHz and DC 500Hz The noise and offset may appear to be slightly higher than shown here if the amplifier input is not differential...

Страница 8: ...ave 300Vpp 1kHz Figure 12 Square wave 300Vpp 20kHz Time ms Output voltage V 150 100 50 0 50 100 150 2 0 1 5 1 0 0 5 0 0 Time ms Output voltage V 150 100 50 0 50 100 150 2 0 1 5 1 0 0 5 0 0 Time s Outp...

Страница 9: ...Vpp step response 10 90 up in 4 4 s Figure 14b 300Vpp step response 10 90 down in 4 2 s Time s Output voltage V 0 4 0 2 0 0 0 2 0 4 100 80 60 40 20 0 Time s Output voltage V 150 100 50 0 50 100 150 10...

Страница 10: ...onse 10 90 down in 3 8 s Figure 14 Unipolar and bipolar step response Figure 15a 0pF load Time s Output voltage V 140 120 100 80 60 40 20 0 10 5 0 5 10 Time s Output voltage V 140 120 100 80 60 40 20...

Страница 11: ...5c 1nF load Figure 15d 10nF load Time s Output voltage V 150 100 50 0 50 100 150 100 80 60 40 20 0 Time s Output voltage V 150 100 50 0 50 100 150 100 80 60 40 20 0 Time s Output voltage V 150 100 50...

Страница 12: ...pacitor can be charged The bandwidth adjustments of the amplifier with different capacitive loads preventing overshoot are clearly visible Note the difference of the horizontal timescale in the figure...

Страница 13: ...Do not dispose of the WMA 200 amplifier as standard waste but bring it to a WEEE electronic waste collection point The amplifier has been built in compliance with the RoHS directive Warranty Falco Sy...

Страница 14: ...ual version User manual version 1 6 Date February 24 2022 Falco Systems Falco Systems BV Remisestraat 1 2225 TH Katwijk aan Zee Phone 31 0 6 21840996 Email info falco systems com Website www falco sys...

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