ML2035

REV. 1.0 10/10/2000

5

FUNCTIONAL DESCRIPTION

The ML2035 is composed of a programmable frequency

generator, a sine wave generator, a crystal oscillator, and a

serial digital interface. The ML2035 frequency and sine

wave generator functional block diagram is shown in

Figure 3.

PROGRAMMABLE FREQUENCY GENERATOR

The programmable frequency generator produces a digital

output whose frequency is determined by a 16-bit digital

word.

The frequency generator is composed of a phase

stored in the data latch is added to the phase accumulator

every 4 cycles of CLK IN. The frequency of the analog

output is equal to the rate at which the accumulator

overflows and is given by the equation:

(1)

The frequency resolution and the minimum frequency are

the same and is given by the following equation:

(2)

Lower frequencies are obtained by using a lower input

clock frequency.

Due to the phase quantization nature of the frequency

generator, spurious tones can be present in the output

range of –55dB relative to fundamental. The energy from

these tones is included in the signal to noise + distortion

specification. The frequency of these tones can be very

close to the fundamental. Therefore, it is not practical to

filter them out.

SINEWAVE GENERATOR

The sinewave generator is composed of a sine look-up

table, a DAC, and an output smoothing filter. The sine

look-up table is addressed by the phase accumulator. The

DAC is driven by the output of the look-up table and

generates a staircase representation of a sine wave.

The output filter smoothes the analog output by removing

the high frequency sampling components. The resultant

harmonic distortion components at least 45dB below the

fundamental.

The ML2035 provides a peak sinewave voltage of

referenced to GND.

The analog section is designed to operate over a range

from DC to 25kHz. Due to slew rate limitations, the peak-

can drive a 1k

Ω, 100pF loads, provided the slew rate

limitations mentioned above are not exceeded.

to-peak output voltage and is specified as:

(3)

CRYSTAL OSCILLATOR

The crystal oscillator generates an accurate reference

clock for the programmable frequency generator. The

internal clock can be generated with a crystal or external

clock.

If a crystal is used, it must be placed between CLK IN and

GND of the ML2035. An on-chip crystal oscillator will

then generate the internal clock. No other external

capacitors or components are required. The crystal should

be a parallel-resonant type with a frequency between

3MHz to 12.4MHz. It should be placed physically as

close as possible to the CLK IN and GND.

An external clock can drive CLK IN directly if desired. The

frequency of this clock can be anywhere between 0 and

12MHz.

The crystal must have the following characteristics:

1. Parallel resonant type

2. Frequency: 3MHz to 12.4MHz

3. Maximum equivalent series resistance of 15

Ω at a drive

levels of 1

µW to 200µW, and 30Ω at drive levels of

10nW to 1

µW

4. Typical load capacitance: 18pF

5. Maximum case capacitance: 7pF

The frequency of oscillation will be a function of the

crystal parameters and PC board capacitance. Crystals that

meet these requirements at 12.352000MHz are M-tron

3709-010 12.352 for 0ºC to 70ºC and 3709-020 12.352

for -40ºC to 85ºC operation.

f

2

23

f

f

MIN

CLKIN

2

22

=

∆