CY8CKIT-059 datasheet(61/140 Pages) INFINEON

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Document Number: 001-84932 Rev. *N

Page 60 of 139

PSoC® 5LP: CY8C58LP Family

Datasheet

8.11 Up/Down Mixer

In continuous time mode, the SC/CT block components are used

to build an up or down mixer. Any mixing application contains an

input signal frequency and a local oscillator frequency. The

polarity of the clock, Fclk, switches the amplifier between

inverting or noninverting gain. The output is the product of the

input and the switching function from the local oscillator, with

frequency components at the local oscillator plus and minus the

signal frequency (Fclk + Fin and Fclk - Fin) and reduced-level

frequency components at odd integer multiples of the local

oscillator frequency. The local oscillator frequency is provided by

the selected clock source for the mixer.

Continuous time up and down mixing works for applications with

input signals and local oscillator frequencies up to 1 MHz.

Figure 8-13. Mixer Configuration

8.12 Sample and Hold

The main application for a sample and hold, is to hold a value

stable while an ADC is performing a conversion. Some

applications

require

multiple

signals

sampled

simultaneously, such as for power calculations (V and I). PSoC

Creator offers a sample and hold component to support this

function.

Figure 8-14. Sample and Hold Topology

(

Φ1 and Φ2 are opposite phases of a clock)

8.12.1 Down Mixer

The S+H can be used as a mixer to down convert an input signal.

This circuit is a high bandwidth passive sample network that can

sample input signals up to 14 MHz. This sampled value is then

held using the opamp with a maximum clock rate of 4 MHz. The

output frequency is at the difference between the input frequency

and the highest integer multiple of the Local Oscillator that is less

than the input.

8.12.2 First Order Modulator - SC Mode

A first order modulator is constructed by placing the switched

capacitor block in an integrator mode and using a comparator to

provide a 1-bit feedback to the input. Depending on this bit, a

reference voltage is either subtracted or added to the input

signal. The block output is the output of the comparator and not

the integrator in the modulator case. The signal is downshifted

and buffered and then processed by a decimator to make a

delta-sigma converter or a counter to make an incremental

converter. The accuracy of the sampled data from the first-order

modulator is determined from several factors. The main

application for this modulator is for a low frequency ADC with

high

accuracy.

Applications

include

strain

gauges,

thermocouples, precision voltage, and current measurement.

Vref

Vout

Rmix 0 20 k or 40 k

sc_clk

Vin

C2 = 1.7 pF

C1 = 850 fF

V i

V ref

V out

Vref

V ref

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