logarithmic amplifier. TDA8780M Datasheet
True logarithmic amplifier
Supersedes data of November 1994
File under Integrated Circuits, IC03
1995 Jul 25
True logarithmic ampliﬁer
• 72 dB true logarithmic dynamic range
• Small-signal gain-adjustment facility
• Constant limiting output voltage
• Temperature and DC power supply voltage independent
• Easy interfacing to analog-to-digital converters
• Output DC level shift facility.
• Dynamic range compression
• IF signal dynamic range reduction in digital receivers
• Compression receivers.
The TDA8780M is a true logarithmic amplifier intended for
dynamic range reduction of IF signals at 10.7 MHz in
digital radio receivers. It offers true logarithmic
characteristics over a 72 dB input dynamic range, has a
small-signal gain-adjustment facility and a constant
limiting output voltage for large input levels.
A unique feature is the smooth “changeover” from linear
operation (inputs less than 60 µV) to logarithmic mode.
The device is manufactured in an advanced BiCMOS
process which enables high performance being obtained
with low DC power supply consumption. The true
logarithmic amplifier can be driven by single-ended or
differential inputs. The DC operating point is set by overall
on-chip feedback decoupled by two off-chip capacitors,
which define the low-frequency cut-off point.
The performance of the amplifier is stabilized against
temperature and DC power supply variations. The
differential output is converted internally to a single-ended
output by an on-chip operational amplifier arrangement in
which the DC output level is set by an externally-supplied
reference voltage. A power-down facility allows the circuit
to be disabled from a control input.
QUICK REFERENCE DATA
supply current in power-down mode
operating input frequency
dynamic logarithmic input voltage (peak value)
operating ambient temperature
SSOP20 plastic shrink small outline package; 20 leads; body width 4.4 mm
1995 Jul 25