Datasheet LT6600-15 (Analog Devices) - 10

LT6600-15
APPLICATIONS INFORMATION Noise
2.5V 0.1μF The noise performance of the LT6600-15 can be evaluated SPECTRUM COILCRAFT ANALYZER with the circuit of Figure 7. R 3 V IN TTWB-1010 IN 1 INPUT – 25Ω 1:1 7 + 4 Given the low noise output of the LT6600-15 and the LT6600-15 2 50Ω 6dB attenuation of the transformer coupling network, it 25Ω 8 – + 5 is necessary to measure the noise fl oor of the spectrum 0.1μF R 6 IN analyzer and subtract the instrument noise from the fi lter 660015 F07 noise measurement. –2.5V Example: With the IC removed and the 25Ω resistors
Figure 7
grounded, Figure 7, measure the total integrated noise (eS) 45 180 NOISE DENSITY, of the spectrum analyzer from 10kHz to 15MHz. With the 40 GAIN = 1x 160 IC inserted, the signal source (V ) NOISE DENSITY, IN) disconnected, and the Hz 35 GAIN = 4x 140 INTEGRA input resistors grounded, measure the total integrated noise /√ INTEGRATED NOISE, 30 120 RMS GAIN = 1x out of the fi lter (e INTEGRATED NOISE, TED NOISE (μ O). With the signal source connected, 25 100 GAIN = 4x set the frequency to 1MHz and adjust the amplitude until Y (nV 20 80 VIN measures 100mVP-P. Measure the output amplitude, 15 60 V V) OUT, and compute the passband gain A = VOUT/VIN. Now 10 NOISE DENSIT 40 compute the input referred integrated noise (eIN) as: 5 20 (e 0 0 0.01 0.1 1 10 100 e O )2 – (eS )2 IN = FREQUENCY (MHz) A 660015 F08
Figure 8. Input Referred Noise, Gain = 1
Table 1 lists the typical input referred integrated noise for various values of RIN. noise power added together, the resulting calculated noise Figure 8 is plot of the noise spectral density as a func- level will be higher than the true differential noise. tion of frequency for an LT6600-15 using the fi xture of
Power Dissipation
Figure 7 (the instrument noise has been subtracted from the results). The LT6600-15 amplifi ers combine high speed with large- signal currents in a small package. There is a need to
Table 1. Noise Performance
ensure that the die junction temperature does not exceed
INPUT REFERRED INPUT REFERRED
150°C. The LT6600-15 package has Pin 6 fused to the
PASSBAND INTEGRATED NOISE INTEGRATED NOISE GAIN (V/V) R
lead frame to enhance thermal conduction when connect-
IN 10kHz TO 15MHz 10kHz TO 30MHz
4 133Ω 36μV ing to a ground plane or a large metal trace. Metal trace RMS 51μVRMS 2 267Ω 62μV and plated through-holes can be used to spread the heat RMS 92μVRMS 1 536Ω 109μV generated by the device to the backside of the PC board. RMS 169μVRMS For example, on a 3/32" FR-4 board with 2oz copper, a The noise at each output is comprised of a differential total of 660 square millimeters connected to Pin 6 of the component and a common mode component. Using a LT6600-15 (330 square millimeters on each side of the PC transformer or combiner to convert the differential outputs board) will result in a thermal resistance, θ to single-ended signal rejects the common mode noise and JA, of about 85°C/W. Without the extra metal trace connected to the gives a true measure of the S/N achievable in the system. V– pin to provide a heat sink, the thermal resistance will Conversely, if each output is measured individually and the be around 105°C/W. Table 2 can be used as a guide when considering thermal resistance. 660015fb 10