Copley amplifier parameter dictionary - Maccon.de
Copley amplifier parameter dictionary - Maccon.de
Copley amplifier parameter dictionary - Maccon.de
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CHAPTER<br />
3: FILTER COEFFICIENTS<br />
There are several <strong>amplifier</strong> <strong>parameter</strong>s which are used to <strong>de</strong>fine filters. These filters are implemented as generic biquadratic filter structures.<br />
Filters of this type implement the following formula to transform the input <strong>parameter</strong> x(n) at time n to an output <strong>parameter</strong> y(n):<br />
y(n) = b0·x(n) + b1·x(n-1) + b2·x(n-2) + a1·y(n-1) + a2·y(n-2)<br />
The values a1, a2, b0, b1, b2 are constants known as filter coefficients. They <strong>de</strong>fine the type of filter being implemented.<br />
The values passed to these <strong>amplifier</strong> filter <strong>parameter</strong>s are used to <strong>de</strong>fine the filter coefficients. The formatting of these <strong>parameter</strong>s varies<br />
<strong>de</strong>pending on the <strong>amplifier</strong> family being interfaced to.<br />
All first generation <strong>Copley</strong> <strong>amplifier</strong>s use 16-bit integer math to implement their filters internally. Filter coefficients are given as 16-bit signed<br />
integer values. To increase the resolution of these coefficients, an additional unsigned scaling coefficient (k) is also specified. The actual<br />
filter formula used within these <strong>amplifier</strong>s is as follows:<br />
y(n) = K · (b0·x(n) + b1·x(n-1) + b2·x(n-2) + a1·y(n-1) + a2·y(n-2)) / 32768 / 4096<br />
To set the filter coefficients on <strong>amplifier</strong>s of this category, 9 words of <strong>parameter</strong> data are passed. The first three words of data are<br />
informational <strong>parameter</strong>s which are used by the CME software to <strong>de</strong>scribe the filter. If the upper 3 bits of the first word are all set then the<br />
filter will be disabled. Other than that, the first three words of data are not used in any way by the firmware. These three words are reserved<br />
for CME use.<br />
Word Description<br />
1 Filter info. Set to 0xFFFF to disable the filter. Otherwise, reserved for CME use.<br />
2 Filter info. Reserved for CME use.<br />
3 Filter info. Reserved for CME use.<br />
4 b2 coefficient.<br />
5 b1 coefficient.<br />
6 b0 coefficient.<br />
7 a2 coefficient.<br />
8 a1 coefficient.<br />
9 K scaler.<br />
<strong>Copley</strong> Controls Page 65