LMH6515 Datasheet, PDF (19/31 Pages) National Semiconductor (TI) – 600 MHz, Digital Controlled, Variable Gain Amplifier

LMH6515
www.ti.com
SNOSAX4C – AUGUST 2007 – REVISED MARCH 2013
ADC Noise Filter
Figure 44 shows a filter schematic and the following table of values are for some common IF frequencies. The
filter shown offers a good compromise between bandwidth, noise rejection and cost. This filter topology is the
same as used on the ADC14V155KDRB High IF Receiver reference design board. This filter topology works best
with the 12 and 14-bit sub-sampling analog to digital converters shown in the Table 2 table.
Filter Component Values
Components
Table 1. Filter Component Values
Fc
BW
L1, L2
L3, L4
C1, C2
C3
L5
R1, R2
75
MHz
40
MHz
10 µH
390 nH
10 pF
22 pF
220 nH
100
140
MHz
20
MHz
10 µH
390 nH
3 pF
41 pF
27 nH
200
170
MHz
25
MHz
10 µH
560 nH
1.4 pF
32 pF
30 nH
100
250
MHz
Narrow Band
10 µH
—
47 pF
11 pF
22 nH
499
5V
AMP V_OUT -
L1
L3
C1
L5
ADC V_IN +
AMP V_OUT +
C2
L4
L2
5V
Figure 45. Sample Filter
ADC V_IN -
ADC V_CM
POWER SUPPLIES
As shown in Figure 46, the LMH6515 has a number of options for power supply connections on the output pins.
Pin 3 (V_CC) is always connected. The output stage can be connected as shown in Figure 47, Figure 48, or
Figure 49. The supply voltage range for V_CC is 4V to 5.25V. A 5V supply provides the best performance while
lower supplies will result in less power consumption. Power supply regulation of 2.5% or better is advised.
Of special note is that the digital circuits are powered from an internal supply voltage of 3.3V. The logic pins
should not be driven above the absolute maximum value of 3.6V. See the DIGITAL CONTROL section for
details.
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