LTC6417 Datasheet, PDF (25/32 Pages) Linear Technology – 1.6GHz Low Noise High Linearity Differential Buffer/ 16-Bit ADC Driver with Fast Clamp

LTC6417
Applications Information
the LTC6417 as a post-amplifier for the LTC5567, it is pos-
sible to achieve IF bandwidths in excess of 500MHz, while
adding bandpass filtering. A key to achieving this extremely
wide IF bandwidth is the use of pre-emphasis inductors
in series with the LTC6417 inputs to compensate for the
inherent rolloff caused by the LTC6417 input capacitance
interacting with the interface impedance. In the example
seen in Figure 14, a value of 33nH for each pre-emphasis
inductor gives excellent wideband performance. Figure 15
shows performance for various values of L. For L = 33nH,
overall conversion gain remains within 1dB from 90MHz
to 590MHz, resulting in 500MHz of IF bandwidth.
Test Circuits
Due to the fully differential design of the LTC6417 and its
usefulness in applications both with and without ADCs, two
test circuits have been used to generate the information
in this data sheet. Test circuit A is DC1660B, a two-port
demonstration circuit for the LTC6417. The board layout
and the schematic are shown in Figures 16 and 17. These
circuits include a 1:4 input balun and a 1:1 output balun
for single-ended-to-differential conversion, allowing direct
analysis using a 2-port network analyzer. Including the input
and output baluns, the –3dB bandwidth is approximately
600MHz. A 1:4 input balun before the LTC6417 inputs
provides 6dB of voltage gain, but results in better noise
figure performance compared to a 1:1 input balun. Noise
figure measurements for both input baluns can be found
in the graphs.
Test circuit B is DC1685A. It consists of an LTC6417 driving
an LTC2209 16-bit 153.6Msps ADC. It is intended for use
in conjunction with DC890B (computer interface board)
and proprietary Linear Technology evaluation software
to evaluate the performance of both parts together. Both
the DC1685A board layout and the schematic can be seen
Figures 18 and 19.
LO
1.65GHz
RF
1.69GHz
TO
2.39GHz
IF+
1nF
L
LTC5567
249Ω
390n
127Ω
V_CC
249Ω
390n
10nF _127Ω
L
IF–
1nF
Figure 14
LTC6417
2
L = 33nH
1
0
L = 18nH
–1
LPF
–2
L = 0nH
–3
–4
–5
–6
–7
40
140 240 340 440 540 640 740
IF FREQUENCY (MHz)
6417 F15
Figure 15
1nF
23.2Ω
23.2Ω _1nF
1:1
IF_OUT
50Ω
6417 F14
6417f
25