Philips tda8785 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

TDA8785

8-bit high-speed analog-to-digital
converter with gain and offset
controls

Preliminary specification
File under Integrated Circuits, IC02

1996 Jan 17

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital
converter with gain and offset controls

FEATURES

• 8-bit analog-to-digital converter (ADC)

• 8-bit digital-to-analog converter (DAC)

• Sampling rate up to 30 Msps for both ADC and DAC

• Binary or two’s complement 3-state TTL outputs

• TTL compatible inputs and outputs

• 100 MHz variable gain amplifier (0 to 20 dB) externally

controlled

• All analog inputs and outputs are differential (can also
be used in single-ended format)

• Analog input signal from 0.1 to 1.0 V (p-p) differential

• Offset amplifier with:

– slow offset control (±250 mV)
– fast offset control (±500 mV) eventually driven by

internal DAC

• ADC output code of 8 (typ.) when analog input signal
and offset correction inputs are 0 V

TDA8785

• Gain, slow offset control inputs and DAC output swing of

1.5 V (p-p) range (2.75 ±0.75 V)

• 2.75 V reference voltage

• Internal references for ADC and DAC.

GENERAL DESCRIPTION

The TDA8785 is an 8-bit analog-to-digital converter with
gain and offset controls for the input signal. An internal
8-bit DAC provides digital adjustment of the different input
offsets.

APPLICA TIONS

• CCD type of systems

• Scanner

• Copier

• Video acquisition.

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

V
V
V
V
I

CCA

I

CCD

I

CCO

CCA1
CCA2
CCD
CCO

analog supply voltage 1 4.75 5.0 5.25 V
analog supply voltage 2 4.75 5.0 5.25 V
digital supply voltage 4.75 5.0 5.25 V
TTL output supply voltage 4.75 5.0 5.25 V
analog supply current − 80 − mA
digital supply current − 30 − mA

TTL output supply current − 9 − mA
INL integral non-linearity 0 to 20 dB gain; ramp input −±0.7 tbf LSB
DNL differential non-linearity 0 to 20 dB gain; ramp input −±0.4 tbf LSB
f

clk(max)

B controlled gain amplifier

maximum clock frequency ADC and DAC 30 −−MHz

− 100 − MHz

bandwidth
P

tot

total power dissipation − 600 − mW

ORDERING INFORMATION

TYPE

NUMBER

NAME DESCRIPTION VERSION

PACKAGE

TDA8785H QFP44 plastic quad flat package; 44 leads (lead length 1.3 mm); body 10 × 10 × 1.75 mm SOT307-2

1996 Jan 17 2

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital converter
with gain and offset controls

BLOCK DIAGRAM

handbook, full pagewidth

V

SOFF(p)

V

SOFF(n)

V

FOFF(p)

V

FOFF(n)

V

FSAD(p)

V

FSAD(n)

V

DACO(p)

V

DACO(n)

V

FSDAC(p)

V

FSDAC(n)

V

i(p)

V

i(n)

43
44
37
38
42
41

39
40

9
8

10
11

V

AMPLIFIER

12 to 19

AGND1

V

CCA

CCA1VCCA2

1 2 3 4

OFFSET

150 Ω 150 Ω

DAC

8

AGND2

GAIN

TDA8785

CLOCK

DRIVER

20 22

CLKDACDA7 to DA0

DEC2

V

V

B

6 7 36 5 35 34

ref

RB

REGULATORS

ADC

DEC1

8

OUTPUTS

CLOCK

DRIVER

OF

TTL

V

CCD

8

23

26 to 33

25
24

21

DGNDCLKADC

TDA8785

AD0 to AD7

V

CCO


OGND

MBG681

Fig.1 Block diagram.

1996 Jan 17 3

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital converter
with gain and offset controls

PINNING

SYMBOL PIN DESCRIPTION

V

CCA1

V

CCA2

AGND1 3 analog ground 1
AGND2 4 analog ground 2
DEC2 5 decoupling input 2
B 6 bandwidth adjustment node input
V

RB

V

DACO(n)

V

DACO(p)

V

FSDAC(p)

V

FSDAC(n)

DA7 12 DAC TTL input; bit 7 (MSB)
DA6 13 DAC TTL input; bit 6
DA5 14 DAC TTL input; bit 5
DA4 15 DAC TTL input; bit 4
DA3 16 DAC TTL input; bit 3
DA2 17 DAC TTL input; bit 2
DA1 18 DAC TTL input; bit 1
DA0 19 DAC TTL input; bit 0 (LSB)
CLKDAC 20 DAC clock input
DGND 21 digital ground
CLKADC 22 ADC clock input
V

CCD

1 analog supply voltage 1 (+5 V)
2 analog supply voltage 2 (+5 V)

7 ADC reference voltage output bottom

(decoupling)
8 DAC negative voltage output
9 DAC positive voltage output

10 DAC full-scale positive control voltage

input

11 DAC full-scale negative control

voltage input

23 digital supply voltage (+5 V)

TDA8785

SYMBOL PIN DESCRIPTION

OGND 24 output ground
V

CCO

AD0 26 output data; bit 0 (LSB)
AD1 27 output data; bit 1
AD2 28 output data; bit 2
AD3 29 output data; bit 3
AD4 30 output data; bit 4
AD5 31 output data; bit 5
AD6 32 output data; bit 6
AD7 33 output data; bit 7 (MSB)
OF 34 output format input
DEC1 35 decoupling input 1
V

ref

V

SOFF(p)

V

SOFF(n)

V

FSAD(p)

V

FSAD(n)

V

FOFF(n)

V

FOFF(p)

V

i(p)

V

i(n)

25 output supply voltage (+5 V)

36 reference voltage output (2.75 V)
37 slow offset amplifier positive voltage

input

38 slow offset amplifier negative voltage

input
39 gain control positive voltage input
40 gain control negative voltage input
41 fast offset amplifier negative voltage

input
42 fast offset amplifier positive voltage

input
43 analog positive voltage input
44 analog negative voltage input

1996 Jan 17 4

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital converter
with gain and offset controls

handbook, full pagewidth

SOFF(n)

FSAD(p)

FSAD(n)

FOFF(n)

FOFF(p)

i(p)

V

CCA1

V

CCA2
AGND1
AGND2

DEC2

V

DACO(n)

V

DACO(p)

V

FSDAC(p)

V

FSDAC(n)

i(n)

V

44

1
2
3
4
5

B

6

V

7

RB

8

9
10
11

V

V

43

42

V

41

V

40

TDA8785

V

V

39

38

SOFF(p)

V

V
37

36

ref

DEC1

35

OF
34

TDA8785

33

AD7

32

AD6

31

AD5
AD4

30

AD3

29
28

AD2
AD1

27

AD0

26

V

25

CCO

OGND

24

V

23

CCD

12

DA7

13

14

15

16

17

DA6

DA5

DA4

DA3

DA2

Fig.2 Pin configuration.

18

DA1

19

DA0

20

21

DGND

CLKDAC

MBG680

22

CLKADC

1996 Jan 17 5

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital converter
with gain and offset controls

FUNCTIONAL DESCRIPTION

The TDA8785 is composed of an 8-bit ADC (30 Msps), a
wide-band gain amplifier, an input offset amplifier and an
8-bit dynamic adjustment DAC.

Input signal

Two input pins are provided to apply a differential input
signal with a wide range (100 to 1000 mV differential). It is
also possible to apply a single signal by setting a DC
voltage on one of the differential pins and supplying the
signal to the other.

Controlled gain amplifier

The gain amplifier is used to adjust the wide input signal
range to the fixed ADC input range of 1 V (p-p).

A large gain of 20 dB can be achieved with low-noise
behaviour and a large bandwidth of 100 MHz to correctly
amplify square type signals with step edges. Using pin 6,
it is possible to reduce the internal bandwidth of the gain
amplifier via an external capacitor and thus improve its
noise behaviour. The gain amplifier is controlled via an
external differential voltage (single input can also be
applied).

TDA8785

The internal 8-bit DAC operates at the ADC clock rate to
allow dynamic corrections on the input signal chain based
on the signal processing information carried out after the
digital conversion. The output voltage amplitude of the
DAC can be controlled via a different input voltage (which
can also be single) in a range of ±25% with a 150 Ω DAC
output load.

The DAC can also be used for the gain or the slow offset
control with some external DC voltage adaptations and
can be considered as a separate function of the ADC
chain. The DAC can be used independently, for example
as a video DAC.

8-bit ADC

The 8-bit ADC converts a signal of 1 V (p-p) from the
controlled gain amplifier into an 8-bit coded digital word at
a maximum rate of 30 Msps. Its reference voltage is
supplied by the general voltage regulator. The output data
format can either be binary, two’s complement or 3-state
by selecting pin OF.

When all the differential inputs on the offset amplifier
(V
0 V (equivalent to both inputs short-circuited), the output
code of the ADC is code 8.

SOFF(p)

, V

SOFF(n)

, V

FOFF(n)

, V

FOFF(p)

, V

i(p)

and V

) are at

i(n)

Input offset amplifier and adjustment DAC

The Input offset amplifier contains two different control
inputs (which can also be single):

• Slow offset control, for slow variation characteristics
(e.g. temperature, supply voltage, etc.)

• Fast offset control, for correction related to the clock
rate.

Slow offset control is carried out by an external voltage
while fast offset control is digitally carried out via the
internal 8-bit DAC with external connections of the
respective pins V

DACO(n)

, V

DACO(p)

, V

FOFF(n)

and V

FOFF(p)

Internal voltage regulator

An internal voltage regulator provides all the references for
the different blocks. A stable 2.75 V voltage reference
output is provided for use in the application environment.
One application is to connect all the slow control inputs
(V

FSDAC(p)

V

FSAD(n)

, V

FSDAC(n)

) to this reference, either to their two differential

, V

SOFF(p)

, V

SOFF(n)

, V

FSAD(p)

inputs to get the nominal settings or to one of the
differential inputs to have easy single-input control.

All these control inputs have the same control range.

.

and

1996 Jan 17 6

Philips Semiconductors Preliminary specification

8-bit high-speed analog-to-digital converter

TDA8785

with gain and offset controls

LIMITING VALUES

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

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT

V

CCA

V

CCD

V

CCO

∆V

CC

V

I

V

clk(p-p)

I

O

T

stg

T

amb

T

j

analog supply voltage −0.3 +7.0 V
digital supply voltage −0.3 +7.0 V
output supply voltage −0.3 +7.0 V
supply voltage difference between

V
V
V

CCA
CCD
CCA

and V
and V
and V

CCD

CCO

CCO

−1.0 +1.0 V

−1.0 +1.0 V

−1.0 +1.0 V

input voltage referenced to AGND −0.3 +7.0 V
clock input voltage for switching (peak-to-peak value) referenced to DGND − V

CCD

V
output current − 6mA
storage temperature −55 +150 °C
operating ambient temperature 0 70 °C
junction temperature − 150 °C

THERMAL CHARACTERISTICS

SYMBOL PARAMETER VALUE UNIT

R

th j-a

thermal resistance from junction to ambient in free air 75 K/W

1996 Jan 17 7