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KH563 参数 Datasheet PDF下载

KH563图片预览
型号: KH563
PDF下载: 下载PDF文件 查看货源
内容描述: 宽带,低失真驱动器放大器 [Wideband, Low Distortion Driver Amplifier]
分类和应用: 驱动器放大器
文件页数/大小: 13 页 / 261 K
品牌: CADEKA [ CADEKA MICROCIRCUITS LLC. ]
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KH563  
DATA SHEET  
With this total value derived, the required external C is  
Gain and Output Impedance Range  
x
developed by backing out the effect of the internal 10pF.  
Figure 7 shows a plot of the recommended gain and  
output impedances for the KH563. Operation outside of  
this region is certainly possible with some degradation in  
performance. Several factors contribute to set this range.  
At very low output impedances, the required value of  
feedback resistor becomes so low as to excessively load  
the output causing a rapid degradation in distortion.  
This, and an expression for the external C without the  
x
intermediate steps are shown below.  
10 C  
t
C =  
x
10 C  
t
or  
The maximum R was set somewhat arbitrarily at 200.  
o
1
2
C =  
pF  
x
This allows the KH563 to drive into a 2:1 step down  
transformer matching to a 50load. (This offers  
some advantages from a distortion standpoint.  
R
o
0.08  
300 1−  
R
g
100  
The plot in Figure 6 shows the required C vs. gain for  
Low Rf or Rg Region  
x
90  
several desired output impedances using the equations  
80  
70  
60  
shown above. Note that for lower R ’s, C can get very  
o
x
large. But, since the total compensation is actually the  
series combination of C and 10pF, going to very high  
Recommended  
Region  
50  
x
C ’s is increasingly ineffective as the total compensation  
40  
x
is only slightly changed. This, in part, sets the lower  
30  
20  
limits on allowable R .  
o
10  
High Noise Region  
20  
0
Maximally Flat Response  
into a Matched Load  
18  
0
20 40 60 80 100 120 140 160 180 200  
Output Impedance ()  
16  
14  
12  
Figure 7: Recommended Gain and  
Output Impedance Range  
Ro = 50Ω  
10  
8
Ro = 75Ω  
6
4
2
0
For a given R , the minimum gain shown in Figure 7 has  
o
been set to keep the equivalent input noise voltage less  
than 4nV/Hz. Generally, the equivalent input noise volt-  
age decreases with higher signal gains. The high gain  
Ro = 100Ω  
5
10 15 20 25 30 35 40 45 50 55  
limit has been set by targeting a minimum R of 10or a  
g
No Load Voltage Gain  
minimum R of 100.  
f
Figure 6: External Compensation Capacitance (C )  
x
Amplifier Configurations  
The KH563 is intended for a fixed, non-inverting, gain  
configuration as shown in Figure 1. The KH560 offers the  
better pulse fidelity with its improved thermal tail in the  
pulse response (vs. the KH563). Due to its low  
internal forward gain, the inverting node does not present  
a low impedance, or virtual ground, node. Hence, in an  
inverting configuration, the signal’s source impedance  
will see a finite load whose value depends on the output  
loading. Inverting mode operation can be best achieved  
using a wideband, unity gain buffer with low output  
impedance, to isolate the source from this varying load.  
A DC level can, however, be summed into the inverting  
node to offset the output either for offset correction  
or signal conditioning.  
A 0% small signal overshoot response can be achieved  
by increasing C slightly from the maximally flat value.  
x
Note that this applies only for small signals due to slew  
rate effects coming into play for large, fast edge rates.  
Beyond the nominal compensation values developed  
thus far, this external C provides a very flexible means  
x
for tailoring the frequency response under a wide variety  
of gain and loading conditions. It is oftentimes useful to  
use a small adjustable cap in development to determine  
a C suitable to the application, then fixing that value for  
x
production. An excellent 5pF to 20pF trimmer cap for this  
is a Sprague-Goodman part #GKX20000.  
When the KH563 is used to drive a capacitive load, such  
as an ADC or SAW device, the load will act to compen-  
Accuracy Calculations  
sate the response along with C . Generally, considerably  
Several factors contribute to limit the achievable KH563  
accuracy. These include the DC errors, noise effects, and  
the impact internal amplifier characteristics have on the  
signal gain. Both the output DC error and noise model  
may be developed using the equivalent model of Figure  
5. Generally, non-inverting input errors show up at the  
x
lower C values are required than the earlier develop-  
x
ment would indicate. This is advantageous in that a low  
R would be desired to drive a capacitive load which,  
o
without the compensating effect of load itself, would  
otherwise require very large C values.  
x
REV. 1A January 2008  
9