2
dc2496aaf
DEMO MANUAL
DC2496A-A/DC2496A-B
operation
Demo Circuit 2496A is a high linearity, fixed gain amplifier.
It is designed for ease of use. The LTC6432-15 is inter-
nally matched to 100Ω differential source and load imped-
ances from 100kHz to 1400MHz. Due to the unpopularity
of 100Ω differential test equipment, transformers have
been added to convert these impedances to single-ended
50Ω. Hence, demo boards with various transformers are
built for corresponding working frequency ranges. The
frequency range of the 2496A evaluation circuit is limited
by these input and output transformers. There are provi-
sions for installing various SMT transformers on either
the top or bottom side of DC2496A’s PCB.
Because LTC6432-15 has a very wide working frequency
range, no single transformer can cover its full 13 octave
frequency band. The DC2496A PCB is quite versatile.
There are footprints for various transformers on the PCB.
Two demo board versions cover most commonly used
frequencies as shown in Table 1.
Table 1. Frequency Ranges and Suggested 2:1 Transformers.
DC NUMBER
FREQUENCY
(MHz)
TRANSFORMER’S
PART #
MANUFACTURER
2496A-A
0.1 to 20
SYTX2-6T-1+
Mini-Circuits
2496A-B
1 to 250
ADT2-1T+
--
20 to 400
ADT2-1T-1P+
--
200 To 950
ADTL2-18+
Please note that the suggested frequency bands are
narrower than small-signal S-Parameters would indicate.
At the edges of their useful band, these transformers
contribute distortion that degrades the performance of
the LTC6432-15.
Figure 1 and Figure 2 show demo board DC2496A-A
and DC2496A-B schematics. Each demo circuit’s sche-
matic shows the required passive support components.
At the board’s inputs and outputs are the low frequency
transformer, SYTX2-6T-1+ or the mid-frequency trans-
former, ADT2-2T+. Each of these transformers has a 1:2
impedance transformation ratio. The input and output DC
blocking capacitors (C7, C9, C12 and C17) are required
because this device is internally DC-biased for optimal
operation. The V
CC
pull-up networks (L1, L2, L3, L4, R1,
R5, R9 and R13) and the de-coupling capacitors (C2, C3,
C4, C5, C19, C20, C21 and C22) provide the proper DC
bias to the RF ±OUT nodes. A single 5V supply is required
for the V
CC
pins on the device.
A pair of stability networks have been added. They consist
of a 1µF capacitor (C6 and C15) and 348Ω resistor (R4
and R14) in parallel at the LTC6432-15 inputs to ensure
low frequency stability.
It is important to note that X8R capacitors are used in
the RF signal path. The DC block and feedback caps have
been specified as X8R capacitors. High capacitance den-
sity (high capacitor values in a small package) typically
contribute distortion products due to their poor voltage
coefficient. Film and NPO capacitors have low distortion
but are unwieldy at 1µF values. As a compromise we have
found that X8R capacitors exhibit low distortion at reason-
able capacitance densities.
If the user is concerned with thermal heating and the
associated reliability, the chip provides a means to deter-
mine the chip temperature. The T_DIODE pin (turret E4)
can be forward biased to ground with 1mA of current. The
measured voltage will be an indicator of the chip junction
temperature (T
J
).
Please note that eight DNC pins are connected on the
demo board. These connections are not utilized for normal
operation and should be left open circuit on the final PCB.
Table 2 shows the function of each input and output on
the board.
Table 2. DC2496A board I/O descriptions
CONNECTOR
FUNCTION
J1 (IN)
Single-ended input. Impedance matched to 50Ω. Drive
from a 50Ω network analyzer or signal source.
J4 (OUT)
Single-ended output. Impedance matched to 50Ω.
Drives a 50Ω network analyzer or spectrum analyzer.
E4 (T_DIODE)
When forward biased, the measured voltage will be an
indicator of the chip junction temperature (T
J
).
E2 (V
CC
)
Positive supply voltage source.
E3 (GND)
Supply ground.
