LMH6401_16 Datasheet, PDF (30/48 Pages) Texas Instruments – LMH6401 DC to 4.5 GHz, Fully-Differential, Digital Variable-Gain Amplifier

LMH6401
SBOS730A – APRIL 2015 – REVISED MAY 2015
www.ti.com
10.1.4 Thermal Considerations
The LMH6401 is packaged in a space-saving UQFN package that has a thermal coefficient (R_θJA) of 78°C/W.
Limit the total power dissipation in order to keep the device junction temperature below 150°C for instantaneous
power and below 125°C for continuous power.
10.2 Typical Application
The LMH6401 is designed and optimized for the highest performance when driving differential input ADCs.
Figure 64 shows a block diagram of the LMH6401 driving an ADC with a fourth-order, low-pass filter. The
primary interface circuit between the amplifier and the ADC is usually an antialiasing filter to suppress high-
frequency harmonics aliasing into the ADC FFT spectrum. The interface circuit also provides a means to bias the
signal to the input common-mode voltage required by the ADC. Filters range from single-order real RC poles to
higher-order RLC filters, depending on the application requirements. Output resistors (R_O) in series with the
amplifier outputs isolate the amplifier from any capacitive load presented by the filter.
Driving Circuit
+
2.5 V
5V
50 Ÿ
50 Ÿ
Tx Line, Z_O = 50 Ÿ 10 Ÿ
R_o+ = 20 Ÿ ^{7.5 nH}
LMH6401
9 pF
Z_IN ~ 100 Ÿ ^{10 Ÿ} VOCM ^{Ro- = 20 Ÿ}
0.01 2F
7.5 nH
18 nH
6.3 pF
18 nH
5 Ÿ
54 Ÿ
54 Ÿ
5 Ÿ
2.8 pF ||1.2 NŸ
AADDSS415B4J4690
V_OCM
0.01 2F
Figure 64. The LMH6401 Driving an ADS54J60 with a 370 MHz Fourth-Order Chebyshev Low-Pass Filter
Low distortion and low noise figure, along-with low power dissipation make the LMH6401 an ideal device for use
in front-end radio applications. Figure 65 shows a block diagram of a one-transmit and one-receive (1T/1R) radio
architecture with a digital pre-distortion path, where the LMH6401 can be used as a variable-gain IF amplifier on
both the transmit and receive signal chain.
Receive Path
LNA
Demodulator
LO1
LMH6401
ADC
CLK1
Modulator
PA
LMH6401
DAC
LO2
LO3
CLK2
CLK3
LMH6401
ADC
Transmit Path
Demodulator
Figure 65. 1T/1R with Digital Pre-Distortion Front-End Radio Application
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