e99a057.pdf

TDA1572

Integrated circuits

Analogue, RF

DATASHEET

10/99

Integrated circuits

Analogue, RF

DATASHEET

10/99

TDA1572

AM Receiver Circuit

AF preamplifier with possibilities

for simple AF filtering

➡ Electronic standby switch

➡ IF output for stereo demodulator and

search tuning.

Manufacturer

Philips Semiconductors

Functional description

General description

The TDA1572 integrated AM receiver circuit performs

all the active functions and part of the filtering

required of an AM radio receiver. It is intended for

use in mains-fed home receivers and car radios. The

circuit can be used for oscillator frequencies up to 50

MHz and can handle RF signals up to 500 mV.

RF radiation and sensitivity to interference are mini-

mized by an almost symmetrical design. The con-

trolled-voltage oscillator provides signals with

extremely low distortion and high spectral purity over

the whole frequency range, even when tuning with

variable capacitance diodes. If required, band switch-

ing diodes can easily be applied. Selectivity is

obtained using a block filter before the IF amplifier.

Gain-controlled RF stage and mixer

The differential amplifier in the RF stage employs an

AGC negative feedback network to provide a wide

dynamic range. Very good cross-modulation behav-

iour is achieved by AGC delays at the various signal

stages. Large signals are handled with low distortion

and the (S+N)/N ratio of small signals is improved.

Low noise working is achieved in the differential

amplifier by using transistors with low base resis-

tance. A double balanced mixer provides the IF out-

put signal to pin 1.

Oscillator

The differential amplifier oscillator is temperature

compensated and is suitable for simple coil connec-

tion. The oscillator is voltage-controlled and has little

distortion or spurious radiation. It is specially suitable

for electronic tuning using variable capacitance

diodes. Band switching diodes can easily be applied

using the stabilized voltage V 13-18 . An extra buffered

oscillator output (pin 12) is available for driving a

synthesizer. If this is not needed, resistor R L(12 ) can

be omitted.

Application example

Poor Man’s Shortwave Receiver, Elektor Electronics

October 1999.

Features

➡ Inputs protected against damage by static dis-

charge

Gain-controlled IF amplifier

This amplifier comprises two cascaded, variable-gain

differential amplifier stages coupled by a band-pass

filter. Both stages are gain-controlled by the AGC

negative feedback network. The IF output is available

at pin 10.

➡

Gain-controlled RF stage

➡

Double balanced mixer

➡

Separately buffered, voltage-controlled and tem-

perature-compensated oscillator, designed for

simple coils

➡

Gain-controlled IF stage with wide AGC range

➡

Full-wave, balanced envelope detector

Detector

The full-wave, balanced envelope detector has very

low distortion over a wide dynamic range. Residual

IF carrier is blocked from the signal path by an inter-

nal low-pass filter.

Internal generation of AGC voltage with possibility

of second-order filtering

➡ Buffered field strength indicator driver

with short-circuit protection

➡

TDA1572

Integrated circuits

Analogue, RF

DATASHEET

10/99

Integrated circuits

Analogue, RF

DATASHEET

10/99

AF preamplifier

This stage preamplifies the audio frequency output

signal. The amplifier output has an emitter follower

with a series resistor which, together with an external

capacitor, yields the required low-pass for AF filter-

ing.

IF stages via suitable AGC delays. The capacitor at

pin 7 can be omitted for low-cost applications.

PARAMETER

SYMBOL

MIN.

TYP.

MAX.

UNIT

Field strength indicator output

A buffered voltage source provides a high-level field

strength output signal which has good linearity for

logarithmic input signals over the whole dynamic

range. If the field strength information is not needed,

R L(11) can be omitted.

Oscillator amplitude (pins 13 to 14)

—

130

150

External load impedance (pins 14 to 13)

R (ext)

0.5

—

200

External load impedance for no oscillation (pins 14 to 13)

R (ext)

—

AGC amplifier

The AGC amplifier provides a control voltage which is

proportional to the carrier amplitude. Second-order

filtering of the AGC voltage achieves signals with very

little distortion, even at low audio frequencies. This

method of filtering also gives fast AGC settling time

which is advantageous for electronic search tuning.

The AGC settling time can be further reduced by

using capacitors of smaller value in the external filter

(C16 and C17). The AGC voltage is fed to the RF and

Ripple rejection at V P(rms) = 100 mV;

f p = 100 Hz (SVRR = 20 log [V15 /V13])

R R

—

Source voltage for switching diodes (6 x V BE ) (pin 13)

—

4.2

—

DC output current (for switching

diodes) (pin 13)

–I O

—

Standby switch

This switch is primarily intended for AM/FM band

switching. During standby mode the oscillator, mixer

and AF preamplifier are switched off.

l 13 = 20 mA

(switch to maximum load) (pin 13)

∆

∆ V I

—

0.3

—

Buffered oscillator output (pin 12)

DC output voltage

V O

—

0.8

—

Short-circuit protection

All pins have short-circuit protection to ground.

Output signal amplitude (peak-to-peak value)

V o(p-p)

—

320

—

Output impedance

Z O

—

170

—

Output current

–I O(peak)

—

Characteristics V P = V 15-18 = 8.5 V; T amb = 25 ° C; f i = 1 MHz; f m = 400 Hz; m = 30%; f IF = 460 kHz;

measured in test circuit, all voltages referenced to ground; unless otherwise specified.

PARAMETER

IF, AGC and AF stages

DC input voltage (pins 3 and 4)

V I

—

2.0

—

IF input impedance (pins 3 to 4)

Z i

2.4

3.0

3.9

SYMBOL

MIN.

TYP.

MAX.

UNIT

IF input capacitance

C i

—

Supply

Supply voltage (pin 15)

IF input voltage for THD = 3% at m = 80% (pins 3 and 4)

V i

—

V P

7.5

8.5

18.0

IF output impedance (pin 10)

Z o

—

Unloaded IF output voltage at V i = 10 mV (pin 10)

V o

Supply current (pin 15)

I P

180

230

290

RF stage and mixer (pins 16 and 17)

DC input voltage

Voltage gain before start of AGC (pins 3 to 4; 6 to 18)

G v

—

V I

—

V P /2

—

AGC range of IF stages: change of V 3-4 for 1 dB change of V o(AF) ;

V 3-4 (ref) = 75 mV

∆ V v

—

RF input impedance at V < 300

Z i

—

5.5

—

AF output voltage at V 3-4(IF) = 50

V o(AF)

RF input capacitance

C i

—

130

—

AF output voltage at V 3-4(IF) = 1 mV

V o(AF)

RF input impedance at V I > 10 mV

Z i

—

310

—

| Z o |

RF input capacitance

C i

—

AF output impedance (pin 6)

2.8

3.5

4.2

IF output impedance (pin 1)

Z o

200

—

Indicator driver (pin 11)

Output voltage at V i = 0 mV; R L = 2.7 k

V o

IF output capacitance

C o

—

140

Output voltage at V i = 500 mV; R L = 2.7 k

V o

Conversion transconductance before start of AGC

I 1 /V i

—

6.5

—

mA/V

2.5

2.8

3.1

R L

Maximum IF output voltage,

inductive coupling to pin 1 (peak-to-peak value)

Load resistance

1.5

—

V 1-15(p-p)

—

Standby switch

Switching threshold at; V P = 7.5 to 18 V, T amb = –40 to +80

DC value of output current; at V I = 0 V (pin 1)

I O

—

1.2

—

V 2-1

AGC range of input stage

—

ON-voltage

—

2.0

RF signal handling capability: (r.m.s. value):

input voltage for THD = 3% at m = 80%

OFF-voltage

V 2-1

3.5

—

20.0

V I (rms)

—

500

—

ON-current at V 2-1 = 0 V

–I 2

—

200

Oscillator

Frequency range

OFF-current at V 2-1 = 20 V

| I 2 |

—

f osc

0.1

—

MHz

Change of output voltage at

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