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Philips AN1651, Application Note

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Philips Semiconductors

Application note

AN1651

Using the NE/SA5234 amplifier

1991 Oct

4

D2

IB2

IB4

IB5

IB6

IB8

IB7

IB9

IB3

VB4

VCC

I2

I1

VEE

D3

CLASS

AB

CONTROL

Q61

Q62

Q83

Q85

Q81

Q82

Q71

Q75

Q72

Q78

Q53,54

Q51,52

C1

C2

C3

C4

C5

R82

C6

Q84

OUTPUT

INPUT

+

–

INTERMEDIATE STAGE

CURRENT CONTROL

CLASS AB OUTPUT

R85

R76

R86

R75

SL00632

Figure  4. 

dB

100

80

60

40

20

0

10Hz

100Hz

1kHz

10kHz

100kHz

1MHz

FREQUENCY

10

106

G1000

SL00633

Figure  5. NE5234 Closed Loop Gain vs Frequency

Summary of Contents for AN1651

Page 1: ... AN1651 Using the NE SA5234 amplifier Author Les Hadley 1991 Oct INTEGRATED CIRCUITS ...

Page 2: ...w 1V transfers the input stage into the P mode of operation In the N mode operating condition collector current from Q1 and Q2 is summed in the output emitter node of Q10 and Q12 respectively Q1 s base is the non inverting input and Q2 s base the inverting input node for the amplifier VCC R10 R11 VB2 Q10 Q12 VB1 IB1 Q2 Q4 Q3 Q5 SWITCH Q9 R8 R9 Q6 Q7 Q8 IP IN VBIAS IN Q2 SL00630 Figure 1 NE5234 Inp...

Page 3: ...m multiple collectors on the non inverting side and provides matching for the following stage Class AB control of the output stage is achieved by Q61 and Q62 with the associated output current regulators These act to monitor the smallest current of the non load supporting output transistor to keep it in conduction Thus neither Q71 or Q81 is allowed to cutoff but is forced to remain in the proper C...

Page 4: ...I1 VEE D3 CLASS AB CONTROL Q61 Q62 Q83 Q85 Q81 Q82 Q71 Q75 Q72 Q78 Q53 54 Q51 52 C1 C2 C3 C4 C5 R82 C6 Q84 OUTPUT INPUT INTERMEDIATE STAGE CURRENT CONTROL CLASS AB OUTPUT R85 R76 R86 R75 SL00632 Figure 4 dB 100 80 60 40 20 0 10Hz 100Hz 1kHz 10kHz 100kHz 1MHz FREQUENCY 10 106 G1000 SL00633 Figure 5 NE5234 Closed Loop Gain vs Frequency ...

Page 5: ...sistor on the non inverting input At 300 Kelvin a 10Ω resistor generates 0 4 nV Hz and the feedback network s equivalent resistance of 90Ω generates 1 2nV Hz Their order of magnitude difference from the main noise sources allows them to be neglected in the overall calculation of total stage noise Noise current is measured across a 47kΩ resistor and averaged in the same manner The thermal noise gen...

Page 6: ...cuits VI MULTIPLE STAGE CONSIDERATIONS Since multiple noise generators are non coherent their total effect is the root of the sum of the squares of the various noise generators at a given amplifier input This makes orders of magnitude lower noise sources less important than the higher magnitude source Therefore when considering the combined signal to noise of multiple stages of gain the first stag...

Page 7: ...er should be biased to half the supply voltage to minimize distortion Operation with dual supplies is simpler from a parts count standpoint as isolation capacitors are not required Also the time constants associated with charging and discharging these is eliminated Figure 10a b and c shows the total harmonic distortion in percent versus input voltage level at 1kHz in VRMS for a non inverting unity...

Page 8: ...se two stages of gain in order to preserve signal quality than to use one high gain stage Of course there is a trade off between the aforementioned factors that affect the signal to noise ratio of the stage and optimizing the Loop gain For example a voice band audio stage which requires 3kHz bandwidth should be limited to a closed loop gain of 40dB for lowest distortion in the output signal For hi...

Page 9: ... be kept at a low AC impedance This is the purpose of bypass capacitor CS Its use provides transient suppression for signals coming from the supply bus A low cost 0 1µF ceramic disk or chip capacitor is recommended for suppressing fast transients in the microsecond and sub microsecond region Foil capacitors are simply too inductive for any high frequency bypass application and should be avoided If...

Page 10: ...gure 16 A 4 20mA Current Loop 4 11 VO 1 3 2 1 2M V2 4 3k 12k 12k 5 0V 1 2MΩ 4 3k 4 3k 1k V2 V1 VO 5 9mV 25 6mV 46 6mV 0 5V 2 50V 4 63V 4 3k S G S G 5 0V S G Matched Strain Gauge elements SL00645 Figure 17 Strain Gauge Amplifier 4 11 1 3 2 4 3k 12kΩ VCC 1 2MΩ 4 3k 4 3k 4 3k SIGNAL COM S G S G 12kΩ Two wire Twisted pair Shielded Line 1 2M SL00646 Figure 18 Remote Strain Gauge CMOS 3V 4 6V DC 4V VR S...

Page 11: ...age combined with a single transistor to drive the current loop The sensitivity is actually in mA V or transconductance which is equal to 1 RSH This sensitivity in this particular example is set to 4mA V Thus with a bridge amplifier having a differential gain of 100 an input of 10mV will produce a 4mA output current and 50mV will produce a 20mA output Of course the line resistance plus receiver re...

Page 12: ...nverting operation is available The inverting input impedance is chosen as 600Ω in order to match standard audio impedance lines within a system The use of two such amplifiers will provide stereo operation to 10dBm for a 600Ω load Voice Operated Microphone The processing of voice transmissions for communications channels is generally coupled with the need for keeping the signal to noise ratio high...

Page 13: ...between the rectifier and the A2 amplifier output AC coupling must be used to isolate the DC common mode voltage of the amplifier from the rectifier storage capacitor and to allow only audio frequencies to drive the switching circuit Amplifier A3 provides a high impedance unity gain buffer to allow a very slow decay rate to be applied to the time constant capacitor CT The output of the storage cap...

Page 14: ...P P This allows for a standardized output level with good characteristics for FM modulation where peak deviation must be controlled Figure 25 shows the input output characteristics of the compressor and ALC The compressor also has an attack time determined by capacitor C6 on Pin 11 Attack time is 10k C6 decay time equals four times this value An auxiliary amplifier stage is used following the NE57...

Page 15: ...ge 3 must then be biased by connecting its non inverting node to bias point A This provides a 2 5V threshold for the proper switching operation of the stage However care must be taken not allow the network s time constant to become code dependent as to the average low frequency signal components or errors will result in the output signal The advantage of this particular circuit is that it has the ...

Page 16: ...RANSMISSION MEDIUM DB dBM 10 68 5 32 25 32 45 32 65 32 85 32 6 68 EXPANDOR OUT COMPRESSION IN VRMS 2 65V 420mV 42mV 4 2mV 1 67V COMPRESSOR OUT EXPANDOR IN REL LEVEL ABS LEVEL 1 2 2 INPUT TO G AND RECT SL00653 Figure 25 NE570 571 SA571 System Level A R 5V 1V 1k 5k 10mV 10k VCC CT RT 100k 2 3 VCC IO CS Rt R1 5V 1 0 5V 4 1k SL00654 Figure 26 Fiber Optic Data Receiver ...

Page 17: ...rs Application note AN1651 Using the NE SA5234 amplifier 1991 Oct 17 3V M ÇÇÇÇÇ ÇÇÇÇÇ ÇÇÇÇÇ ÇÇ ÇÇ ÇÇ ÇÇ ÇÇÇÇ ÇÇÇÇ ÇÇÇÇ ÇÇÇÇ 3V 4 11 1N9683 6 5 7 9 10 8 2 3 1 13 12 14 NE5234 1 100 1N9683 SL00655 Figure 27 Half Bridge Servo ...

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