TI-TL852.pdf
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SLSS003 − SEPTEMBER 1983 − REVISED MARCH 1988
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
POST OFFICE BOX 1443
• HOUSTON, TEXAS 77251−1443
D Designed for Use With the TL851 in Sonar
Ranging Modules Like the SN28827
D Digitally Controlled Variable-Gain
Variable-Bandwidth Amplifier
D Operational Frequency Range of 20 kHz
to 90 kHz
D TTL-Compatible
D Operates From Power Sources of 4.5 V
to 6.8 V
D Interfaces to Electrostatic or Piezoelectric
Transducers
D Overall Gain Adjustable With One External
Resistor
description
The TL852 is an economical sonar ranging receiver integrated circuit for use with the TL851 control integrated
circuit. A minimum of external components is required for operation, and this amplifier easily interfaces to
Polaroid’s 50-kHz electrostatic transducer. An external 68-kΩ ±5% resistor from BIAS to GND provides the
internal biasing reference. Amplifier gain can be set with a resistor from G1IN to GADJ. Required amplifier gain
will vary for different applications. Using the detect-level measurement circuit of Figure 1, a nominal
peak-to-peak value of 230 mV input during gain step 2 is recommended for most applications. For reliable
operation, a level no lower than 50 mV should be used. The recommended detect level of 230 mV can be
obtained for most amplifiers with an R1 value between 5 kΩ and 20 kΩ
Digital control of amplifier gain is provided with gain control inputs GCA, GCB, GCC, and GCD. These inputs
must be driven synchronously (all inputs stable within 0.1 µs) to avoid false receive output signals due to invalid
logic counts. This can be done easily with the TL851 control integrated circuit. A plot showing relative gain for
the various gain steps versus time can be seen in Figure 2. To dampen ringing of the 50-kHz electrostatic
transducer, a 5-kΩ resistor from G1IN to XIN is recommended.
An external parallel combination of inductance and capacitance between LC and V
CC
provides an amplifier with
an externally controlled gain and Q. This not only allows control of gain to compensate for attenuation of signal
with distance, but also maximizes noise and sidelobe rejection. Care must be taken to accurately tune the L-C
combination at operating frequency or gain and Q will be greatly reduced at higher gain steps.
AC coupling between stages of the amplifier is accomplished with a 0.01-mF capacitor for proper biasing.
The receive output is normally held at a low level by an internal 1-µA current source. When an input of sufficient
amplitude is received, the output is driven alternately by the 1-µA discharge current and a 50-µA charging
current. A 1000-pF capacitor is required from REC to GND to integrate the received signal so that one or two
noise pulses will not be recognized.
XIN provides clamping for the transformer secondary when used for transducer transmit drive as shown in
Figure 4 of the SN28827 data sheet.
The TL852 is characterized for operation from 0°C to 40°C.
Copyright 1988, Texas Instruments Incorporated
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G1IN
XIN
GADJ
LC
V
CC
G1OUT
G2IN
BIAS
GND
GCD
GCA
GCB
GCC
NC
NC
REC
N PACKAGE
(TOP VIEW)
NC − No internal connection
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