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HSP45116AVC-52Z

Numerically Controlled Oscillator/Modulator

Intersil 

HSP45116A

Applications

The NCOM can be used for Amplitude, Phase and

Frequency modulation, as well as in variations and

combinations of these techniques, such as QAM. It is most

effective in applications requiring multiplication of a rotating

complex sinusoid by an external vector. These include AM

and QAM modulators and digital receivers. The NCOM

implements AM and QAM modulation on a single chip, and

is a element in demodulation, where it performs complex

down conversion. It can be combined with the Intersil

HSP43220 Decimating Digital Filter to form the front end of a

digital receiver.

Modulation/Demodulation

Figure 4 shows a block diagram of an AM modulator. In this

example, the phase increment for the carrier frequency is

loaded into the Center Frequency Register, and the

modulating input is clocked into the real input of the CMAC,

with the imaginary input set to 0. The modulated output is

obtained at the real output of the CMAC. With a sixteen bit,

two’s complement signal input, the output will be a 16-bit real

number, on ROUT0-15 (with OUTMUX = 00).

SIGNAL INPUT

16 RIN

32

CLK

PFCS

SIN

CMAC

16

NCOM

16 RO

MODULATED OUTPUT

LO

FIGURE 4. AMPLITUDE MODULATION

By replacing the real input with a complex vector, a similar

setup can generate QAM signals (Figure 5). In this case, the

carrier frequency is loaded into the Center Frequency

Register as before, but the modulating vector now carries

both amplitude and phase information. Since the input vector

and the internally generated sine and cosine waves are both

16 bits, the number of states is only limited by the

characteristics of the transmission medium and by the

analog electronics in the transmitter and receiver.

The phase and amplitude resolution for the Sine/Cosine

Section (16-bit output), delivers a spectral purity of greater

than 90dBc. This means that the unwanted spectral

components due to phase uncertainty (phase noise) will be

greater than 90dB below the desired output (dBc, decibels

below the carrier). With a 32-bit phase accumulator in the

Phase/Frequency Control Section, the frequency tuning

resolution equals the clock frequency divided by 232. For

example, a 25MHz clock gives a tuning resolution of

0.006Hz.

32

CLK

PFCS

NCOM

RIN IMIN

16

16

16

CMAC

16

16 RO

D/A LO

FIGURE 5. QUADRATURE AMPLITUDE MODULATION (QAM)

The NCOM also works with the HSP43220 Decimating

Digital Filter to implement down conversion and low pass

filtering in a digital receiver (Figure 6). The NCOM performs

complex down conversion on the wideband input signal by

multiplying the input vector and the internally generated

complex sinusoid. The resulting signal has components at

twice the center frequency and at DC. Two HSP43220s, one

each on the real and imaginary outputs of the HSP45116A,

perform low pass filtering and decimation on the down

converted data, resulting in a complex baseband signal.

HSP45116A

NCOM

COS (wt)

HSP43220

DDF

SAMPLED

INPUT

DATA

INPUT

SIN (wt)

NCOM

OUTPUT

DDF

OUTPUT

0 10MHz

0

20MHz

0

FIGURE 6. CHANNELIZED RECEIVER CHIP SET

14

FN4156.4

May 7, 2007

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