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PCM56

DISCUSSION OF

SPECIFICATIONS

The PCM56 is specified to provide critical performance

criteria for a wide variety of applications. The most critical

specifications for D/A converter in audio applications are

Total Harmonic Distortion, Differential Linearity Error,

Bipolar Zero Error, parameter shifts with time and

temperature, and settling time effects on accuracy.

The PCM56 is factory-trimmed and tested for all critical key

specifications.

The accuracy of a D/A converter is described by the transfer

function shown in Figure 1. Digital input to analog output

relationship is shown in Table I. The errors in the D/A

converter are combinations of analog errors due to the linear

circuitry, matching and tracking properties of the ladder and

scaling networks, power supply rejection, and reference

errors. In summary, these errors consist of initial errors

including Gain, Offset, Linearity, Differential Linearity, and

Power Supply Sensitivity. Gain drift over temperature rotates

the line (Figure 1) about the bipolar zero point and Offset

drift shifts the line left or right over the operating temperature

range. Most of the Offset and Gain drift with temperature or

time is due to the drift of the internal reference zener diode.

The converter is designed so that these drifts are in opposite

directions. This way the Bipolar Zero voltage is virtually

unaffected by variations in the reference voltage.

DIGITAL INPUT CODES

The PCM56 accepts serial input data (MSB first) in the

Binary Two’s Complement (BTC) form. Refer to Table I

for input/output relationships.

FIGURE 1. Input vs Output for an Ideal Bipolar D/A Con-

verter.

BIPOLAR ZERO ERROR

Initial Bipolar Zero Error (Bit 1 “on” and all other bits “off”)

is the deviation from 0V out and is factory-trimmed to

typically

±30mV at +25°C.

DIFFERENTIAL LINEARITY ERROR

Differential Linearity Error (DLE) is the deviation from an

ideal 1LSB change from one adjacent output state to the

next. DLE is important in audio applications because

excessive DLE at Bipolar Zero (at the “major carry”) can

result in audible crossover distortion for low level output

signals. Initial DLE on the PCM56 is factory trimmed to

typically

±0.001% of FSR. The MSB DLE is adjustable to

zero using the circuit shown in Figure 6.

POWER SUPPLY SENSITIVITY

Changes in the DC power supplies will affect accuracy.

The PCM56 power supply sensitivity is shown by Figure 2.

Normally, regulated power supplies with 1% or less ripple

are recommended for use with the DAC. See also Power

Supply Connections paragraph in the Installation and

Operating Instructions section.

SETTLING TIME

Settling time is the total time (including slew time) required

for the output to settle within an error band around its final

value after a change in input (see Figure 3).

Settling times are specified to

±0.006% of FSR: one for a

large output voltage change of 6V and one for a 1LSB

change. The 1LSB change is measured at the major carry

(0000 hex to ffff hex), the point at which the worst-case

settling time occurs.

DIGITAL INPUT

ANALOG OUTPUT

Binary Two’s

Voltage (V),

Current (mA),

Complement (BTC)

DAC Output

VOUT Mode

IOUT Mode

7FFF Hex

+ Full Scale

+2.999908

–0.999970

8000 Hex

– Full Scale

–3.000000

+1.000000

0000 Hex

Bipolar Zero

0.000000

0.000000

FFFF Hex

Zero –1LSB

–0.000092

+0.030500

µA

TABLE I. Digital Input to Analog Output Relationship.

Frequency (Hz)

1

86

80

74

68

62

56

52

46

40

34

28

10

100

1k

10k

100k

Negative Supplies

Positive Supplies

FIGURE 2. Power Supply Sensitivity.

Gain

Drift

Offset

Drift

Bipolar

Zero

0111...1111

0111...1110

0000...0010

0000...0001

0000...0000

1111...1111

1111...1110

1000...0001

1000...0000

–FSR/2

Analog Output

(+FSR/2) –1LSB

All Bits On

* See Table I for digital code definitions.