Texas Instruments Evaluation Kit for the LMH6518 LMH6518SQEVK/NOPB LMH6518SQEVK/NOPB 데이터 시트
제품 코드
LMH6518SQEVK/NOPB
LMH6518
+OUT
100
:
DC Coupled Hi-Z
Input Instrument
-
OUT
DC Coupled Hi-Z
Input Instrument
Miscellaneous
Figure 2. LMH6518 Output Observation With Hi-Z Instrumentation
3. Input(s): Ensure that the LMH6518 inputs (LMH6518 pins 6 and 7) are both close to V
CC
/2 (= 2.5 V)
and there is less than 1 mV of difference in voltage between them. On the board, use a DC voltmeter
to measure LMH6518 pin 6 and 7 voltages (or C
to measure LMH6518 pin 6 and 7 voltages (or C
14
and R
19
, right hand side pads). LMH6518 pin 6
potential (driven input) can be controlled by varying the incoming signal offset (2.5 V nominal) at J3
(SMA connector). If the two LMH6518 inputs are not offset close to each other, as stated, measured
results could be affected. Some of the side-effects of input offset are: output clipping, excess distortion,
loss of bandwidth, or step response anomalies.
(SMA connector). If the two LMH6518 inputs are not offset close to each other, as stated, measured
results could be affected. Some of the side-effects of input offset are: output clipping, excess distortion,
loss of bandwidth, or step response anomalies.
Potentiometer R
25
(board bottom side) is provided to null any remnant output offset, especially useful
when the LMH6518 operating conditions change. For an effective method of input offset adjustment,
especially when the LMH6518 is set for high gain (HG/ 0 dB), monitor J1 and J2 (outputs) SMA center
pins (1.2 V nominal) with a DVM set to read DC voltage and adjust R
especially when the LMH6518 is set for high gain (HG/ 0 dB), monitor J1 and J2 (outputs) SMA center
pins (1.2 V nominal) with a DVM set to read DC voltage and adjust R
25
to minimize the voltage
difference between these two outputs to less than 50 mV. This will reduce any input offset so that the
output can be observed.
output can be observed.
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Miscellaneous
1. Overlapping gain state: As shown in
, one of the possible gain states (18.8 dB) is covered by
either preamp HG, or preamp LG. This gain is possible with preamp set to high gain and 20 dB ladder
attenuation, or, with preamp set to low gain and 0 dB ladder attenuation. Choose preamp high gain
(with 20 dB ladder attenuation) for best noise performance or preamp low gain (with 0 dB ladder
attenuation) for best distortion performance
attenuation, or, with preamp set to low gain and 0 dB ladder attenuation. Choose preamp high gain
(with 20 dB ladder attenuation) for best noise performance or preamp low gain (with 0 dB ladder
attenuation) for best distortion performance
Table 2. LMH6518 Gain Map
Attenuation (dB)
Preamp Gain
0
2
4
6
8
10
12
14
16
18
20
Lo
18.8
16.8
14.8
12.8
10.8
8.8
6.8
4.8
2.8
0.8
−
1.16
Hi
38.8
36.8
34.8
32.8
30.8
28.8
26.8
24.8
22.8
20.8
18.8
2. LMH6518 Evaluation Software Look:
Ladder Attenuator: 0 dB to 20 dB. 10 steps. Each step is 2 dB
Total Gain: This displays the total device gain (read only, assuming 100
Total Gain: This displays the total device gain (read only, assuming 100
Ω
differential load across J2
and J1 SMA or J8 and J7 outputs) based on the preamp gain and the ladder attenuation selected
Filters: Full (no filter), 20 MHz, 100 MHz, 200 MHz, 350 MHz, 650 MHz, and 750 MHz.
Power Mode: Full power and Aux Hi-Z (with Aux Hi-Z, the auxiliary output is turned off with
approximately 60 mA reduction in 5 V supply current)
Preamp Gain: Hi gain and low gain (with 20 dB difference between the two)
Write: To write the current setup on the GUI screen into the LMH6518 registers. To change any of the
LMH6518 operating registers, the adjustments should be made first, followed by a single click on the
“Write” button.
Read: To read back all LMH6518 registers for confirmation and verification. If the register Read back is
different from the last Write state, the software displays an alert window.
Exit: To close the application
Filters: Full (no filter), 20 MHz, 100 MHz, 200 MHz, 350 MHz, 650 MHz, and 750 MHz.
Power Mode: Full power and Aux Hi-Z (with Aux Hi-Z, the auxiliary output is turned off with
approximately 60 mA reduction in 5 V supply current)
Preamp Gain: Hi gain and low gain (with 20 dB difference between the two)
Write: To write the current setup on the GUI screen into the LMH6518 registers. To change any of the
LMH6518 operating registers, the adjustments should be made first, followed by a single click on the
“Write” button.
Read: To read back all LMH6518 registers for confirmation and verification. If the register Read back is
different from the last Write state, the software displays an alert window.
Exit: To close the application
4
AN-1906 LMH6518 Evaluation Board
SNOA535B – October 2008 – Revised May 2013
Copyright © 2008–2013, Texas Instruments Incorporated