TS615IPWT datasheet(22/27 Pages) STMICROELECTRONICS

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TS615

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POWER SUPPLY BYPASSING

A proper power supply bypassing comes very im-

portant for optimizing the performance in high fre-

quency range. Bypass capacitors should be

placed as close as possible to the IC pins to im-

prove high frequency bypassing. A capacitor

greater than 1

µF is necessary to minimize the dis-

tortion. For a better quality bypassing a capacitor

of 10nF is added following the same condition of

implementation. These bypass capacitors must be

incorporated for the negative and the positive sup-

ply.

Figure 63 : Circuit for Power Supply Bypassing

SINGLE POWER SUPPLY

The following figure show the case of a 5V single

power supply configuration

Figure 64 : Circuit for +5V single supply

The TS615 operates from 12V down to 5V power

supplies. This is achieved with a dual power sup-

ply of ±6V and ±2.5V or a single power supply of

12V and 5V referenced to the ground. In the case

of this asymmetrical supplying, a new biasing is

necessary to assume a positive output dynamic

range between 0V and +VCC supply rails. Consid-

ering the values of VOH and VOL, the amplifier will

provide an output dynamic from +0.5V to 10.6V on

Ω load for a 12V supplying, from 0.45V to 3.8V

on 10

Ω load for a 5V supplying.

The amplifier must be biased with a mid supply

(nominally +VCC/2), in order to maintain the DC

component of the signal at this value. Several op-

tions are possible to provide this bias supply (such

as a virtual ground using an operational amplifier),

or a two-resistance divider which is the cheapest

solution. A high resistance value is required to lim-

it the current consumption. On the other hand, the

current must be high enough to bias the non-in-

verting input of the amplifier. If we consider this

bias current (30

µA max.) as the 1% of the current

through the resistance divider to keep a stable mid

supply, two resistances of 2.2k

Ω can be used in

the case of a 12V power supply and two resistanc-

es of 820

Ω can be used in the case of a 5V power

supply.

The input provides a high pass filter with a break

frequency below 10Hz which is necessary to re-

move the original 0 volt DC component of the input

signal, and to fix it at +VCC/2.

CHANNEL SEPARATION - CROSSTALK

The following figure show the crosstalk from an

amplifier to a second amplifier. This phenomenon,

accented in high frequencies, is unavoidable and

intrinsic of the circuit.

Nevertheless, the PCB layout has also an effect

on the crosstalk level. Capacitive coupling be-

tween signal wires, distance between critical sig-

nal nodes, power supply bypassing, are the most

significant points.

Figure 65 : Crosstalk vs. Frequency

AV=+4, Rfb=620Ω, VCC=±6V, Vout=2Vp

-VCC

+VCC

µF

10nF

TS615

µF

10nF

-VCC

+VCC

µF

10nF

TS615

µF

10nF

820

Ω

+5V

Rload

OUT

Rfb

910

Ω

µF

+ 1

µF

½ TS615

100

µF

820

Ω

+5V

10nF

Rin

Ω

820

Ω

+5V

Rload

OUT

Rfb

910

Ω

µF

+ 1

µF

½ TS615

100

µF

820

Ω

+5V

10nF

Rin

Ω

10k

100k

10M

-130

-120

-110

-100

-90

-80

-70

-60

-50

Frequency (Hz)

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