LMH6503MAX Datasheet, PDF (23/33 Pages) Texas Instruments – LMH6503 Wideband, Low Power, Linear Variable Gain Amplifier

LMH6503
www.ti.com
SNOSA78E – OCTOBER 2003 – REVISED APRIL 2013
Table 1. V_G Definition Based on V^−
V_G
Definition
Expression (V)
V_{G_MIN}
Gain Cut-off
0.2 x V^−
V_{G_MID}
A_VMAX/2
0
V_{G_MAX}
A_VMAX
−0.2 x V^−
b) V_{G_LIMIT} (maximum permissible voltage on V_G) is reduced. This is due to limitations within the device
arising from transistor headroom. Beyond this limit, device performance will be affected (non-destructive).
Referring to Figure 67, note that with V⁺ = 2.5V, and V^− = −4V, V_{G_LIMIT} is approaching V_{G_MAX} and already
"Max gain" is reduced by 1dB. This means that operating under these conditions has reduced the
maximum permissible voltage on V_G to a level below what is needed to get Max gain. If supply voltages
are asymmetrical, reference Figure 67 and Figure 68 plots to make sure the region of operation is not
overly restricted by the "pinching" of V_{G_LIMIT}, and V_{G_MAX} curves.
c) "Max_gain" reduces. There is an intrinsic reduction in max gain when the total supply voltage is reduced
(see Figure 43). In addition, there is the more drastic mechanism described in "b" above and shown in
Figure 67.
Similar plots for V⁺ = 5V operation are shown in Figure 68 for comparison and reference.
1.6
MAX GAIN
1.4
20.5
20
1.2
19.5
V_G LIMIT
1
19
0.8
0.6
0.4
0.2
0
-4.5
V⁺ = 2.5V
R_F = 1k:
R_G = 170:
-4 -3.5 -3
V^- (V)
V_G MAX
18.5
18
17.5
17
16.5
-2.5
-2
Figure 67. V_{G_MAX(,VV+ G=_L2IM.5ITV, )&} Max-gain vs. V^-
5
4.5 ^VG ^LIMIT
4
3.5
3 ^{MAX GAIN}
2.5
2
1.5
1
0.5
0
-6
V_G MAX
-5.5 -5
-4.5
V^- (V)
20.5
20.4
20.3
20.2
20.1
V⁺ = 5V
R_F = 1k:
R_G = 170:
20
19.9
19.8
19.7
19.6
19.5
-4 -3.5 -3
Figure 68. V_{G_MAX},(VV_{+G_=LI5MVIT),} & Max-gain vs. V^-
Copyright © 2003–2013, Texas Instruments Incorporated
Product Folder Links: LMH6503
Submit Documentation Feedback
23