LMH6514_14 Datasheet, PDF (20/29 Pages) Texas Instruments – LMH6514 600 MHz, Digital Controlled, Variable Gain Amplifier

LMH6514
SNOSB06 – JANUARY 2008
www.ti.com
The output common mode voltage is not self biasing, it needs to be pulled up to the positive supply rail with
external inductors as shown in Figure 42. This gives the LMH6514 the capability for large signal swings with very
low distortion on a single 5V supply. The internal load resistors provide the LMH6514 with very consistent gain.
A unique internal architecture allows the LMH6514 to be driven by either a differential or single ended source. If
driving the LMH6514 single ended the unused input should be terminated to ground with a 0.01 µF capacitor.
Directly shorting the unused input to ground will disrupt the internal bias circuitry and will result in poor
performance.
5V
680 nH
390 nH ^{3 pF}
41 pF 27 nH 200:
390 nH
3 pF
200
680 nH
ADC C_IN
5V
Center Frequency is 140 MHz with a 20 MHz Bandwidth
Designed for 200Ω Impedance
Figure 50. Bandpass Filter
ADC Noise Filter
Below is a filter schematic and a table of values for some common IF frequencies. The filter shown below offers
a good compromise between bandwidth, noise rejection and cost. This filter topology is the same as is 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
Fc
BW
Components
L1, L2
L3, L4
C1, C2
C3
L5
R1, R2
Table 1. Filter Component Values
75 MHz
40 MHz
10 µH
390 nH
10 pF
22 pF
220 nH
100
140 MHz
20 MHz
10 µH
39 0nH
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
20
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