LMH6503MAX Datasheet, PDF (18/33 Pages) Texas Instruments – LMH6503 Wideband, Low Power, Linear Variable Gain Amplifier

LMH6503
SNOSA78E – OCTOBER 2003 – REVISED APRIL 2013
www.ti.com
CHOOSING R_F AND R_G
R_G is calculated using Equation 5. V_INPUTMAX is the maximum peak input voltage (V_pk) determined by the
application. I_RGMAX is the maximum allowable current through R_G and is typically 2.3mA. Once A_VMAX is
determined from the minimum input and desired output voltages, R_F is then determined using Equation 6. These
values of R_F and R_G are the minimum possible values that meet the input voltage and maximum gain constraints.
Scaling the resistor values will decrease bandwidth and improve stability.
V_INPUTMAX
R_G = _IRGMAX
(5)
1
R_F = _{K *} R_{G *} A_VMAX
(6)
Figure 60 illustrates the resulting LMH6503 bandwidths as a function of the maximum ( y axis) and minimum
(related to x axis) input voltages when V_OUT is held constant at 1V_PP.
10
10MHz ^{5MHz 2.7MHz}
1
150MHz
100MHz
0.1
V_OUT = 1V_PP
V_G = V_GMAX
I_RGMAX = 2.3mA
0.01
1
50MHz
10
A_VMAX (V/V)
20MHz
100
Figure 60. Bandwidth vs. V_INMAX and A_VMAX
ADJUSTING OFFSETS
Treating the offsets introduced by the input and output stages of the LMH6503 is accomplished with a two step
process. The offset voltage of the output stage is treated by first applying −1.1V on V_G, which effectively isolates
the input stage and multiplier core from the output stage. As illustrated in Figure 61, the trim pot located at R14
on the LMH6503 Evaluation Board (LMH730033) should then be adjusted in order to null the offset voltage seen
at the LMH6503's output (pin 10).
18
Submit Documentation Feedback
Product Folder Links: LMH6503
Copyright © 2003–2013, Texas Instruments Incorporated