LT5554_15 Datasheet, PDF (1/32 Pages) Linear Technology – Broadband Ultra Low Distortion 7-Bit Digitally Controlled VGA

FEATURES
n _{1GHz Bandwidth at all Gains}
n _{48dBm OIP3 at 200MHz, 2VP-P into 50Ω,}
R_OUT = 100Ω
n _{–88dBc IMD3 at 200MHz, 2VP-P into 50Ω,}
R_OUT = 100Ω
n _{1.4nV/√Hz Input-Referred-Noise (RTI)}
n _{20dBm Output P1dB at 70MHz, ROUT = 130Ω}
n _{2dB to 18dB Gain Range (ROUT = 50Ω)}
n _{0.125dB Gain Step Size}
n _{30ps Group Delay Variation}
n _{5ns Fast Gain Settling Time}
n _{5ns Fast Overdrive Recovery}
n _{–80dB Reverse Isolation}
APPLICATIONS
n _{Differential ADC Driver}
n _{IF Sampling Receivers}
n _{VGA IF Power Amplifier}
n _{50Ω Driver}
n _{Instrumentation}
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LT5554
Broadband Ultra Low
Distortion 7-Bit Digitally
Controlled VGA
DESCRIPTION
The LT^®5554 is a 7-bit digitally controlled programmable
gain (PG) amplifier with 16dB gain control range. It
consists of a 50Ω input variable attenuator, followed by
a high linearity variable transconductance amplifier. The
coarse 4dB input attenuator step is implemented via 2-bits
of digital control (PG5, PG6). The fine transconductance
amplifier 0.125dB step within 3.875dB gain control range
is set via 5-bits digital control (PG0 to PG4). The LT5554
gain control inputs (PGx) and the STROBE input can be
directly coupled to TTL or ECL drivers. The seven parallel
gain control inputs time skew can be eliminated by using
the STROBE input positive transition.
The internal output resistor R_O = 400Ω limits the maxi-
mum overall gain to 36dB for open outputs. The internal
circuitry of open output collectors enables the LT5554 to
be unconditionally stable over any loading conditions (in-
cluding external SAW filters) and provides –80dB reverse
isolation at 300MHz.
The LT5554 is internally protected during overdrive and
has an on-chip power supply regulator.
With 0.125dB step resolution and 5ns settling time, the
LT5554 is suitable in applications where continuous gain
control is required.
TYPICAL APPLICATION
RF
INPUT
LO
5V
V_CC MODE
0.1μF
IF
IF
BPF
AMPLIFIER
0.1μF
C_DEC
0.1μF
IN⁺ _–
DEC
LT5554
BPF
+
IN^–
7 BITS
PGx GAIN CONTROL
STROBE
OIP3 and SFDR vs Frequency
132
49
R_OUT = 50Ω
130
46
OIP3
ADC
128
43
5554 TA01
SFDR
126
0
50
100
150
FREQUENCY (MHz)
40
200
5554 TA01b
5554f
1