Datasheet TDA8780M Datasheet (Philips)

INTEGRATED CIRCUITS

DATA SH EET

TDA8780M

True logarithmic amplifier

Product specification
Supersedes data of November 1994
File under Integrated Circuits, IC03

1995 Jul 25

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

FEATURES

• 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.

APPLICATIONS

• Dynamic range compression

• IF signal dynamic range reduction in digital receivers

• Compression receivers.

GENERAL DESCRIPTION

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

SYMBOL PARAMETER MIN. TYP. MAX. UNIT

V

P

I

P

I

P(PD)

f

in

V

in(M)

T

amb

supply voltage 4.5 5.0 5.5 V
supply current −−6.7 mA
supply current in power-down mode −−250 µA
operating input frequency −−15 MHz
dynamic logarithmic input voltage (peak value) 0.06 − 300 mV
operating ambient temperature −20 − +75 °C

ORDERING INFORMATION

PACKAGE

TYPE NUMBER

NAME DESCRIPTION VERSION

TDA8780M SSOP20 plastic shrink small outline package; 20 leads; body width 4.4 mm SOT266-1

1995 Jul 25 2

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

BLOCK DIAGRAM

book, full pagewidth

C

C

C

V
V

C

CE

DEC1

DEC2

V

P

11

6

lf

in
in

lf

100 k

1
20

100 k

15

16

3

CONTROL

18

R

100 k

Ω

Ω

100 k

Ω

20 k

Ω

20 k

Ω

Ω

20 k

20 k

Ω

13

8

Ω

17

TDA8780M

45 19

R

g

GND1 GND2 GND3 GND4 GND5

g

141072

V

out

V

ref

TEST

MBE161

Fig.1 Block diagram.

1995 Jul 25 3

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

PINNING

SYMBOL PIN DESCRIPTION

V

in

GND1 2 ground 1
C

DEC1

R

g

R

g

C

lf

GND2 7 ground 2
V

ref

n.c. 9 not connected
GND3 10 ground 3 (main ground)
V

P

n.c. 12 not connected
V

out

GND4 14 ground 4
C

lf

CE 16 TTL-level-compatible circuit enable

TEST 17 test input; connected to ground in

C

DEC2

GND5 19 ground 5
V

in

1 signal voltage input

3 control circuit first decoupling and

optional start-up capacitor connection
4 small-signal gain-setting resistor
5 small-signal complementary

gain-setting resistor
6 low-frequency cut-off point setting

capacitor

8 external reference voltage input

11 power supply

13 true logarithmic voltage output

15 complementary low-frequency cut-off

point setting capacitor

input (active HIGH)

normal operation

18 control circuit second decoupling and

optional start-up capacitor

20 complementary signal voltage input

handbook, halfpage

V

1

in

GND1

2

C

3

DEC1

R

4

g

R

5

g

C

GND2

V

ref

n.c. n.c.

GND3

TDA8780M

6

lf

7
8
9

10

MBE160

Fig.2 Pin configuration.

V

20

in

GND5

19

C

18

DEC2

17

TEST
CE

16

C

15

lf

14

GND4
V

13

out

12

V

P

11

1995 Jul 25 4

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

FUNCTIONAL DESCRIPTION

A true logarithmic amplifier can be realized from a cascade
of similar stages each stage consisting of a pair of
amplifiers whose inputs and outputs are connected in
parallel. One of these amplifiers can be formed by an
undegenerated long-tailed pair which provides high gain
but limited linear input signal-handling capability. The
other amplifier can be formed by a degenerated long-tailed
pair which provides a gain of unity and a much larger linear
input signal-handling capability.

The overall cascade amplifies very small input signals but,
once these reach the level at which the undegenerated
long-tailed pair in the last stage is at the limit of its linear
signal-handling capability, the output voltage becomes
logarithmically dependent on the input signal level. This
behaviour continues until the input signal reaches the level
at which undegenerated long-tailed pair in the first stage is
at the limit of its linear input signal-handling capability. The
transfer characteristic beyond this point then depends on
the exact configuration of the degenerated long-tailed pair
in the first stage.

Five stages are used in the TDA8780M to provide a 72 dB
true logarithmic dynamic range. The DC bias current in the
undegenerated long-tailed pair in the first stage is made
externally adjustable, using an off-chip resistor, to provide
a small-signal gain adjustment facility. The small signal
gain defined by this resistor is valid when the IC is
operating in the “linear” mode, for input signals typically
less than 60 µV.

A high-level limiter is inserted between the first and second
stages to provide a constant limiting output voltage which
is essentially independent of the value of the gain setting
resistor. These stages 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 is stabilized against temperature and DC
power supply variations. The input to the true logarithmic
amplifier is protected against damage due to excessive
differential input signals by diodes.

The differential output from the true logarithmic amplifier 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.
The output is capable of driving loads down to 10 kΩ. The
limiting output voltage and the output drive capability have
been chosen to facilitate interfacing to analog-to-digital
converters. A major part of the DC power supply current
consumption of the device is associated with provision of
this output drive capability. The DC power supply
consumption is significantly less when the device is driving
smaller loads.

A power-down facility allows the circuit to be disabled from
a TTL-level compatible control input.

1995 Jul 25 5

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

SYMBOL PARAMETER MIN. MAX. UNIT

V

P

V

i

T

amb

T

stg

HANDLING

Inputs and outputs are protected against electrostatic discharge in normal handling. However, to be totally safe, it is
desirable to take normal precautions appropriate to handling MOS devices.

supply voltage −0.3 +6.0 V
input voltage all other pins referenced to ground −0.3 VP+ 0.3 V
operating ambient temperature −20 +75 °C
IC storage temperature −55 +150 °C

ESD in accordance with

“MIL STD 883C” -“Method 3015”

.

CHARACTERISTICS

V

=5V; T

P

=25°C; V

amb

= 2.5 V; Vinat fin= 10.7 MHz; Rg= 3.3 kΩ; output not loaded; unless otherwise specified.

ref

Signal values expressed as peak voltages mV (peak), µV (peak) or dBm (50 Ω).

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
Supply

V

P

I

P

I

P(PD)

t

sw

supply voltage 4.5 5.0 5.5 V
supply current VP= 5.5 V; Vin=1V − 5.4 6.7 mA

= 5.0 V; Vin=1V − 4.9 6.2 mA

V

P

supply current in power-down output not loaded − 40 200 µA

R

=10kΩ−100 250 µA

L

switching time see Fig.6 − 70 −µs

Reference input (pin 8)

V

ref

R

ref

external reference voltage input 2.0 2.5 VP− 2.0 V
external reference resistance input − 40 − kΩ

Inputs (pins 1 and 20)

f

in

R

diff

input operating frequency note 1 1.0 10.7 15 MHz
differential small-signal input

Vin=10mV − 10 − kΩ

resistance

C

diff

V

in(min)

differential input capacitance − 2 − pF
input voltage level at start of

− 60 −µV

logarithmic characteristic

V

in(top)

input voltage level at top end of

− 300 − mV

logarithmic characteristic

V

in(max)

maximum input signal voltage input protection diodes not

− 1 − V

conducting

∆V

in

input voltage level spread across

over whole T

and VP range −±2.5 − dB

amb

logarithmic range

1995 Jul 25 6

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
Output (pin 13)

V

os

V

out

DC offset voltage (V
output voltage level across

logarithmic range

V

out(lim)

limiting output voltage Vin= 1 V (+13.0 dBm) 750 950 1050 mV

∆ϕ spread in output phase transfer

characteristic across logarithmic
range

f

lf

G

flat

R

13

low frequency cut-off point (3 dB) see Fig.6 −−0.1 MHz
gain flatness at 1 to 15 MHz Vin=10mV − 0.5 1.5 dB
output resistance − 150 −Ω

Logic input (pin 16)

V

IL

V

IH

I

LI

LOW level input voltage 0 − 0.8 V
HIGH level input voltage 2 − V
input leakage current VIL=0toV

Note

1. With some changes in application the lower input frequency limit can be lowered.

out

to V

) no input signal −60 +40 +140 mV

ref

Vin=60µV (−71.4 dBm) 45 80 115 mV
V

= 400 µV (−54.9 dBm) 200 245 290 mV

in

V

= 3 mV (−37.4 dBm) 365 440 495 mV

in

= 25 mV (−19.0 dBm) 530 610 690 mV

V

in

V

= 200 mV (−1.0 dBm) 680 780 880 mV

in

V

= 300 mV (+2.6 dBm) 710 820 930 mV

in

R

= 0; Vin= 3 mV; see Fig.3 − 530 − mV

g

R

= ∞; Vin= 3 mV; see Fig.3 − 360 − mV

g

− 15 −

P

−1 − +1 µA

P

V

1995 Jul 25 7

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

1000

handbook, halfpage

V

out

(mV)

800

600

400

200

0

80 20

VCC= 5 V; V

60 40 20 0

= 2.5 V; fin= 10 MHz; T

ref

Fig.3 Output voltage dependence on Rg.

MLD209

R = 0

g

R = 3.3 kΩ

g

∞

R =

g

V (dBm, 50 Ω)

in

=25°C.

amb

1000

handbook, halfpage

V

out

(mV)

800

600

400

200

0

80 20

60 40 20 0

Fig.4 Typical transfer characteristics.

MGC118

V (dBm, 50 Ω)

in

Rg =

MGC666

∞

100

handbook, halfpage

V

out

(mV)

75

50

25

0

0 100

Rg = 0 Rg = 3.3 kΩ

50

Vin (µV)

Fig.5 Typical small signal gain.

1995 Jul 25 8

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

APPLICATION INFORMATION

The circuit is typically connected as shown in Fig.6. The
single-ended 10.7 MHz input IF signal is applied
(arbitrarily) to one of the two input pins via a ceramic filter.
These inputs should not be DC coupled as this will disable
the on-chip feedback which sets the DC operating point of
the true logarithmic amplifier. The relatively high
impedance of these inputs facilitates correct termination of
the ceramic filter by an off-chip resistor.

IF input

IF filter 10.7 MHz

330 Ω

3.3 kΩ

100 pF

100 pF

56 pF

C

V

GND1

DEC1

R

R

C

in

1

2

3

g

4

g

5

lf

6

handbook, full pagewidth

The low-frequency cut-off point is determined by the value
of capacitors connected to pins 6 and 15 which decouple
the overall DC feedback and the value of the input coupling
capacitors. The output is coupled to an analog-to-digital
converter thus the value of the voltage fed to the reference
voltage input is not critical. It could be useful in other
applications, where the output may be DC coupled to an
alternative analog-to-digital converter, to derive this
reference voltage from the centre of the input resistor
chain of the analog-to-digital converter.

100 pF

V

in

20

GND5

19

C

DEC2

18

17

16

TDA8780M

15

TEST

CE

C

lf

33 pF

56 pF

circuit
enable
input

GND2 GND4

7

V

ref

2.5 V

8

n.c. n.c.

9

GND3

10

Fig.6 Typical application diagram.

1995 Jul 25 9

14

13

12

11

MGC117

V

out

V

P

output to
ADC

5 V

47 nF2.2 nF

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

PACKAGE OUTLINE

SSOP20: plastic shrink small outline package; 20 leads; body width 4.4 mm

D

c

y

Z

20

pin 1 index

11

A

2

A

1

110

w M

b

e

p

E

H

E

detail X

SOT266-1

A

X

v M

A

Q

(A )

L

p

L

A

3

θ

0 2.5 5 mm

scale

DIMENSIONS (mm are the original dimensions)

UNIT A1A2A

mm

Note

1. Plastic or metal protrusions of 0.20 mm maximum per side are not included.

A

max.

1.5

OUTLINE
VERSION

SOT266-1

0.1501.4

1.2

b

3

p

0.32

0.20

0.20

0.13

0.25

IEC JEDEC EIAJ

(1)E(1)

cD

6.6

6.4

REFERENCES

4.5

0.65 1.0 0.2

4.3

1995 Jul 25 10

eHELLpQZywv θ

6.6

6.2

0.75

0.45

0.65

0.45

PROJECTION

0.13 0.1

EUROPEAN

(1)

0.48

0.18

ISSUE DATE

90-04-05
95-02-25

o

10

o

0

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

SOLDERING
Introduction

There is no soldering method that is ideal for all IC
packages. Wave soldering is often preferred when
through-hole and surface mounted components are mixed
on one printed-circuit board. However, wave soldering is
not always suitable for surface mounted ICs, or for
printed-circuits with high population densities. In these
situations reflow soldering is often used.

This text gives a very brief insight to a complex technology.
A more in-depth account of soldering ICs can be found in
our

“IC Package Databook”

Reflow soldering

Reflow soldering techniques are suitable for all SO
packages.

Reflow soldering requires solder paste (a suspension of
fine solder particles, flux and binding agent) to be applied
to the printed-circuit board by screen printing, stencilling or
pressure-syringe dispensing before package placement.

Several techniques exist for reflowing; for example,
thermal conduction by heated belt. Dwell times vary
between 50 and 300 seconds depending on heating
method. Typical reflow temperatures range from
215 to 250 °C.

(order code 9398 652 90011).

During placement and before soldering, the package must
be fixed with a droplet of adhesive. The adhesive can be
applied by screen printing, pin transfer or syringe
dispensing. The package can be soldered after the
adhesive is cured.

Maximum permissible solder temperature is 260 °C, and
maximum duration of package immersion in solder is
10 seconds, if cooled to less than 150 °C within
6 seconds. Typical dwell time is 4 seconds at 250 °C.

A mildly-activated flux will eliminate the need for removal
of corrosive residues in most applications.

Repairing soldered joints

Fix the component by first soldering two diagonally­opposite end leads. Use only a low voltage soldering iron
(less than 24 V) applied to the flat part of the lead. Contact
time must be limited to 10 seconds at up to 300 °C. When
using a dedicated tool, all other leads can be soldered in
one operation within 2 to 5 seconds between
270 and 320 °C.

Preheating is necessary to dry the paste and evaporate
the binding agent. Preheating duration: 45 minutes at
45 °C.

Wave soldering

Wave soldering techniques can be used for all SO
packages if the following conditions are observed:

• A double-wave (a turbulent wave with high upward
pressure followed by a smooth laminar wave) soldering
technique should be used.

• The longitudinal axis of the package footprint must be
parallel to the solder flow.

• The package footprint must incorporate solder thieves at
the downstream end.

1995 Jul 25 11

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

DEFINITIONS

Data sheet status

Objective specification This data sheet contains target or goal specifications for product development.
Preliminary specification This data sheet contains preliminary data; supplementary data may be published later.
Product specification This data sheet contains final product specifications.

Limiting values

Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or
more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation
of the device at these or at any other conditions above those given in the Characteristics sections of the specification
is not implied. Exposure to limiting values for extended periods may affect device reliability.

Application information

Where application information is given, it is advisory and does not form part of the specification.

LIFE SUPPORT APPLICATIONS

These products are not designed for use in life support appliances, devices, or systems where malfunction of these
products can reasonably be expected to result in personal injury. Philips customers using or selling these products for
use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such
improper use or sale.

1995 Jul 25 12

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

NOTES

1995 Jul 25 13

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

NOTES

1995 Jul 25 14

Philips Semiconductors Product specification

True logarithmic amplifier TDA8780M

NOTES

1995 Jul 25 15

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413061/1500/02/pp16 Date of release: 1995 Jul 25
Document order number: 9397 750 00234